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SCIENTIFIC REVOLUTION

00-1800

IE FORMATION

THE

ODERN

ATTITUDE

A. R. HALL

m

I

THE SCIENTIFIC REVOLUTION

THE SCIENTIFIC

REVOLUTION1500-1800The Formation

of the Modern

ScientificAttitude

A. R. HALLLecturer in the History of Science, University

of Cambridge, and Fellow of Christ's College.

THE BEACON PRESS BOSTON

First published 1954

First Beacon Paperback edition published \ 956,

by arrangement with Longmans, Green and Company

PRINTED IN U.S.A.

Third Printing, June

Collegia Christi, suasori meo necnon auctori,

grato ammo

PREFACETo the historian of science the University of Cambridge offers

riches in its manuscripts, its libraries, and its associations. Amongthose who dwell in the places once frequented by Newton, Darwin

and Rutherford there are many who, quietly and unostentatiously,

are making their contributions to the understanding of this age

of science m terms of its long historical evolution. No one who

has lived with them, no one moreover who has been fortunate

enough to learn from Charles Raven, Herbert Butterfield, and

Joseph Needham, can be other than conscious of indebtedness.

To them, and to all those friends who have helped or tolerated

my endeavours, I offer my grateful thanks. One other only I

mention by name, since he is no longer with us, Robert Stewart

Whipple, ^hose life-long enthusiasm for the history of science is

commemorated in the collection of historic scientific instruments

which he presented to this University.

Above all, this volume could not have been written without

the consistent support of my College, which has given generous

encouragement to the study of the history of science, and the

interest with which the University has fostered the teaching of

this subject.

CHRIST'S COLLEGE, A. P.. HALLCAMBRIDGE

February 1954

I have taken advantage of the reprinting of this volume by

the Beacon Press to correct some mistakes and oversights. I

express my gratitude to all who have drawn my attention to

such imperfections.

A. R. H.

CONTENTSINTRODUCTION page xi

Chapter 1 Science in 1500 i

[I New Currents in the Sixteenth Century 34

III The Attack on Tradition : Mechanics 73

IV The Attack on Tradition : Astronomy 102

V Experiment in Biology 129

VI The Principles of Science in the early Seven-

teenth Century 159

VII The Organization of Scientific Inquiry 186

VIII Technical Factors in the Scientific Revolution 217

IX The Principate of Newton 244

X Descriptive Biology and Systematics 275

XI The Origins of Chemistry 303

XII Experimental Physics in the Eighteenth

Century 339

CONCLUSION 364

Appendices : A. Botanical Illustration 369

B. Comparison of the Ptolemaic and Coperni-can Systems 370

C. Scientific Books before 1500 371

BIBLIOGRAPHICAL NOTES 375

INDEX 381

INTRODUCTION

IHAVE tried in this book to present something in the nature of

a character-study, rather than a biographical outline, of the

scientific revolution. Natural science may be defined suffi-

ciently for my purpose as the conscious, systematic investigationof the phenomena revealed in the human environment, and in

man himself objectively considered. Such investigation alwaysassumes that there is in nature a regular consistency, so that

events are not merely vagarious, and therefore an order or pattern

also, to which events conform, capable of being apprehended bythe human mind. But science in this sense is not simply the productof one attitude to nature, of one set of methods of inquiry, or of

the pursuit of one group of aims. Within it there is room for both

economic and religious motives, for a greater or less exactitude in

observation (though some measure of systematic and repeatedobservation is essential to science), and for a considerable latitude

in theorization.

In many of these respects modern science differs markedly from

that of a not very remote past. It demands rigorous standards

in observing and experimenting. By insisting that it deals onlywith material entities in nature, it excludes spirits and occult

powers from its province. It distinguishes firmly between theories

confirmed by multiple evidence, tentative hypotheses and un-

supported speculations. It presents, not a possible or even a

plausible picture of nature, but one in which all available facts

are given their logical, orderly places. These are the most impor-tant characteristics of modern science, which it acquired duringthe period of transition conveniently known as the scientific

revolution, and has since retained. Certainly they were long in

gestation, but it is with the period of their coming to fruition andvindication by success that this volume is concerned. Some topicsI have chosen to omit: mathematics, because it deals not with the

phenomena of nature, but with numbers; medicine, because it

was at this time rather an art than a natural science. It has not

xii INTRODUCTION

been my object to attempt a complete narration of events, nor to

dwell on biographical and experimental details. Perhaps these

omissions may be forgiven in a book designed as an introduction

to the study of the historical processes at work in the developmentof science, and of the major stages in that development.

Science began soon after the birth of civilization, Man's attemptto win an Empire over Nature (in Francis Bacon's phrase) was

much older still; he had already learnt to domesticate animals

and plants, to shape inorganic materials like clay and metals to

his purposes, and even to mitigate his bodily ailments. We do not

know how or why he did these things, for his magic and his

reasoning are equally concealed. Only with the second millen-

nium B.C. is it possible to discern, dimly, the beginnings of

science in the coalescence of these three elements in man's

attitude to Nature empirical practice, magic and rational

thinking.The same three elements continued to exist in science for many

thousand years, until the scientific revolution took place in the

sixteenth and seventeenth centuries. Reason, in conjunction with

observation and experiment, slowly robbed magic of its power,and was gradually better able to anticipate and absorb the chance

discoveries of inventive craftsmen, but complete reliance upon a

rational scientific method in man's reaction to his natural environ-

ment is very recent. Magic and esoteric mystery the elements of

the irrational were not firmly disassociated from serious science

before the seventeenth century, at which time even greater stress

than before was being laid on the usefulness to scientists of the

craftsman's practical skills. This in turn was not outgrown until

the nineteenth century, when it became clear that in the future

sheer empiricism and chance would add little to man's natural

knowledge, or to his natural power.Rational science, then, by whose methods alone the phenomena

of nature may be rightly understood, and by whose applicationalone they may be controlled, is the creation of the seventeenth and

eighteenth centuries. Since then dramatic achievements in under-

standing and power have followed successively. In this sense the

period 1500-1800 was one of preparation, that since 1800 one of

accomplishment. And it is convenient to conclude this history of

the scientific revolution with the early years of the nineteenth

INTRODUCTION xiii

century for other reasons. Though profound changes in scientific

thought have occurred since that time, and though the growth of

complexity in both theory and experimental practice has been

prodigious, the processes, the tactics and the forms by which

modern science evolves have not changed. However great the

revision of ideas of matter, time, space and causality enforced

during the last half-century, it was a revision of the content, not

the structure of science. In its progress since 1800 the later

discoveries have always embraced the earlier: Newton was not

proved wrong by Einstein, nor Lavoisier by Rutherford. Theformulation of a scientific proposition may be modified, andlimitations to its applicability recognized, without affecting its

propriety in the context to which it was originally found appro-

priate. We do not need sledge-hammers to crack nuts; we do not

need the Principle of Indeterminacy in calculating the future

position of the moon: 'the old knowledge, as the very means for

coming upon the new, must in its old realm be left intact; onlywhen we have left that realm can it be transcended.' 1

Despite the progressive accumulation ofknowledge and elabora-

tion of theory, only the broader extrapolations of nineteenth-

century science would now be described blankly as"wrong,"

though a larger part of its picture of Nature might be described

as "inadequate" or as "true within certain limits." Even in

biology, where ancient and extra-scientific notions lingered long,where experiment was most tardy in finding its just deployment,this is still the case. The systematic and descriptive biology of the

pre-Darwinian epoch was not rendered futile by the theory of

evolution. Earlier microscopists were not exposed to ridicule by the

founders of cytology. On the contrary, the revolution in thoughtabout animate nature incorporated, and was founded on, the

labours of three or four generations. The same could not be said

of science before 1500, or even, without restriction, of the science

of the seventeenth and eighteenth centuries. Its progress in these

earlier times was not by accretion, for it was now and again

necessary to jettison encumbering endowments from the past.

Such science was on occasion simply wrong, both in fact and in

interpretation. Its propositions had to be rejected in toto>not

merely circumscribed, as the result of experiment and creative

1J. Robert Oppenheimer, in his third Reith Lecture (The Listener, vol. L,

P- 943).

xiv INTRODUCTION

thinking. In this respect the beginning of the nineteenth centuryseems a useful point of demarcation between the scientific

revolution, in the course of which the sciences painfully and in

succession acquired their cumulative character, and the recent

period during which that character has been successfully

maintained.

The cumulative growth of science, arising from the employmentof methods of investigation and reasoning which have been

justified by their fruits and their resistance to the corrosion of

criticism, cannot be reduced to any single theme. We cannot say

why men are creative artists, or writers, or scientists; why some

men can perceive a truth, or a technical trick, which has eluded

others. From the bewildering variety of experience in its social,

economic and psychological aspects it is possible to extract onlya few factors, here and there, which have had a bearing on the

development of science. At present, at least, we can only describe,

and begin to analyse, where we should like to understand. The

difficulty is the greater because the history of science is not, andcannot be, a tight unity. The different branches of science are

themselves unlike in complexity, in techniques, and in their

philosophy. They are not all affected equally, or at the same time,

by the same historical factors, whether internal or external. It is

not even possible to trace the development of a single scientific

method, some formulation of principles and rules of operatingwhich might be imagined as applicable to every scientific inquiry,for there is no such thing. Methods of research in each subjectare too closely bound up with the content and problems of that

subject for the devising of a mechanical method.

Nor can we always exploit any dichotomy between the ideas

and the practice of science, though this dichotomy may be a

useful tool at times. Interpretations without knowledge and

knowledge without interpretations are equally unbalanced and

sterile; any branch of science consists of both. Therefore, since

knowledge arises from practical operations, the history of science

can never be a purely intellectual history (like that of mathe-

matics), nor can it be analysed in a wholly logical manner. For

ideas arise from facts, and the facts of science may be revealed in

an order conditioned by chance, by technical resourcefulness, or

industrial invention. On the other hand, the creative intellect is

always playing upon the materials provided by techniques of

INTRODUCTION xv

experiment, observation or measurement; however subtle these

become, they can never be said to determine the course of a

science, unless in a negative sense.

The dichotomy in science, the fact that its progress requires

both conceptual imagination and manipulative ingenuity, is

particularly apparent in the scientific revolution, and presents

peculiar problems. The reaction against the traditional pictureof Nature derived from the Greeks occurred simultaneously on

the factual and the interpretative levels. The theories ofthe past were

criticized as being inconsistent, speculative, incomprehensible,and as involving spiritual qualities rather than the properties of

matter; the facts related in the past were challenged as ill-tested,

spurious, superstitious, and as casually chosen without care in

observation and experiment. The development of each of these

phases of criticism may be traced in the later middle ages, when,

however, they were rarely associated. Even after 1500 manyexponents of a new attitude failed to perceive that doubts of fact

and theory were inter-related; that one could not proceed without

the other. Hence a great part of the force of the "new philosophy"of the seventeenth century was due to its dual scepticism, its

ambition to challenge fact and theory, sometimes without

consciousness of making a double attack. This duality reinforced

attention to the question of the logical connection between facts

and theories, which had also been examined by medieval critics

of Aristotle. How were the relevant facts to be brought to light?

How, with the facts known, were appropriate propositions

concerning them to be arrived at? How could scientific proposi-tions be tested by their usefulness in dealing with facts? The earlysuccess of the scientific revolution owed much to the answeringof such questions (pragmatically, rather than philosophically) in

the scientific method combining observation, hypothesis, experi-ment and mathematical analysis, a method which demonstrates

in itself the essential liaison between the factual and interpretativelevels of inquiry.

If the scientific revolution cannot be completely depicted,even in its origins, as an intellectual revolt against the traditional

interpretation of Nature, nevertheless such a revolt demands

primacy of place in tracing its antecedents. Few men have, or had,the sense of supremacy of pure fact demanded by Francis Bacon.

The majority of scientists at all times have sought for facts with

xvi INTRODUCTION

an object in view. Consequently, the scientific empiricists of the

seventeenth century, including Bacon himself, pointed to the

insufficiency of contemporary science before they clamoured for

more facts on which to frame a sounder doctrine. They did not

need these facts to teach them Aristotle's mistakes, for of those

they were already aware; they needed observations and experi-ments to avoid falling into fresh errors of their own. Cartesians,

too, were as confident that conventional science was untrust-

worthy: because it ignored the method of reasoning from in-

dubitable truths, and was therefore philosophically unsubstantial.

And does not Galileo himself refute Aristotle with reason, before

overwhelming him by experiment? Medieval science, and

especially the Aristotelean doctrines within it, was not so much

swept away by a hurricane of uncomfortable facts, as broughtdown by its own internal decay. While the mechanics of Greek

science, the four elements, the bodily humours, the Ptolemaic

system, still commanded allegiance (though becoming less andless relevant to practical affairs) the Hellenistic view of the cosmos

was becoming increasingly alien to the European mind. From the

fourteenth to the sixteenth century men might teach and work in

science as though they were Greeks of antiquity, but they were not

so in fact, and the community of thought between Europe andHellas grew ever more formal. By 1600 it was almost academic.

A demonstration in Greek mathematics or a particular piece of

reasoning could fire admiration, but the universe could be seen

through Aristotle's eyes no more. Even his expositors had trans-

formed him.

In part this was brought about by the rival Christian authority.No Christian could ultimately escape the implications of the fact

that Aristotle's cosmos knew no Jehovah. Christianity taughthim to see it as a divine artifact, rather than as a self-contained

organism. The universe was subject to God's laws; its regularities

and harmonies were divinely planned, its uniformity was a result

ofprovidential design. The ultimate mystery resided in God rather

than in Nature, which could thus, by successive steps, be seen not

as a self-sufficient Whole, but as a divinely organized machine in

which was transacted the unique drama of the Fall and Redemp-tion. If an omnipresent God was all spirit, it was the more easyto think of the physical universe as all matter; the intelligences,

spirits and Forms of Aristotle were first debased, and then

INTRODUCTION xvii

abandoned as unnecessary in a universe which contained nothingbut God, human souls and matter.

Christianity furnished the scientist with God as the First Cause

of things. But if this First Cause had, so to speak, set the universe

to run its course and endowed man with free-will to make his

own destiny, the phenomena of nature could only be the result of

determined processes, manifestations of a mechanistic design, like

an infinitely complex automaton or clock. A clock is not explained

by saying that the hands have a natural desire to turn, or that the

bell has a natural appetite for striking the hours, but by tracingits movements to the interconnections of its parts, and so to the

driving force, the weight. If God was the driving force in the

universe, were not its motions and other properties also to be

ascribed to the interconnections of its parts? The question, slowly

compelling attention over three hundred years, received a positive

answer in the seventeenth century. The only sort of explanationscience could give must be in terms of descriptions of processes,

mechanisms, interconnections of parts. Greek animism was dead.

Appetites, natural tendencies, sympathies, attractions, were mori-

bund concepts in science, too. The universe of classical physics,

in which the only realities were matter and motion, could begin to

take shape.

CHAPTER I

SCIENCE IN 1500

EUROPEAN

civilization at the beginning of the sixteenth centurywas isolated as it had not been since the first revival of learn-

ing some four hundred years earlier. Political changes hadsevered traditional links between east and west. The heart of the

great area of Islamic culture, from which medieval scholarshipand science had drawn their inspiration, had been over-run bythe Turks; the eastern Christian centre of Byzantium, the last

direct heir of ancient Greece, was destroyed; the learned Moorsand Jews of Spain were expelled by the armies of Castille and

Aragon. The overland route to China, by which many importantinventions had been transmitted to Europe, among them the

new instruments of learning, paper and printing, and over whichMarco Polo had passed, was now barred. Against this loss of a

relatively free interchange of ideas and commodities through the

Mediterranean may be set a developing commercial and scientific

interest in the promise of geographical exploration across the

oceans. The Portuguese had brought spices from the Indies;

Spain had drawn her first golden tribute from Hispaniola. But

the results of the re-orientation of communications southwards

and westwards upon the Atlantic had not yet been assimilated,

and though Europeans were quick to recognize the value of

negroes or American Indians as slaves, they had not yet learnt to

appreciate the magnitude of the civilizations in India and Chinawith which, for the first time, they came into direct contact.

Fortunately, when these events occurred, European scholars

had already emerged from their tutelage, and Latin literature,

having been enriched with almost everything that Arabic was to

convey to it, had become creative in its own right. The final

dissolution of the Christian empire in the Near East, indeed,

brought to Europe a direct knowledge of classical science with

which it had been less perfectly acquainted through the Islamic

intermediary. At the moment when their intellectual communionwith other peoples was most sharply denied by circumstance, the

2 THE SCIENTIFIC REVOLUTION

humanistic scholars of the renaissance were most engrossed in

studying the pure origins of western civilization in Greece andRome. During the next centuries the trend of the middle ages wasto be reversed; Europeans were to teach the East far more than

they learned from it.

In 1500 the fruitful cultivation of science was^ limited to western

Europe, to a small region of the whole civilized world stretching

from Salamanca to Cracow, from Naples to Edinburgh. Even the

peripheries of this region were illuminated rather by the reflected

brilliance of the Italian renaissance, than by any great achieve-

ments of their own. The northern shift of the focus of learning was

beginning northern Italy had replaced the south and Sicily as the

cultural centre of Europe but the sixteenth is unquestionably the

Italian century in science. Scholars, mathematicians, physicians

everywhere measured their own attainments by Italian standards;

the Italian universities, and the Italian printing-houses, possessedan acknowledged pre-eminence. Beneath inevitable gradations in

civilization (no less marked in science than in fine art) lay an

essential cultural unity, undisturbed by nationalism or religious

schism. Europe had a common tradition; in matters temporal it

was consciously the heir of Greece and Rome, shaping the texture

and manner of its own life to the model of their golden age; in

matters spiritual a single compass of belief had passed from the

great Councils of the Church through the early Fathers to the

Papacy and the medieval Doctors. If the secular Empire hadbecome a shadow, the spiritual power of the Church seemed still

firmly founded upon a single theology and a universal orthodoxywhich had triumphed over Albigenses, Wyclif and Hus. Uponthis unified Church all learning was in varying degrees depen-

dent; the universities, themselves papal creations, were religious

institutions. The study of medicine was the only discipline able to

stand, to some extent, detached from learning's prime duty to

theology, and even the teaching and practice of medicine were

subject to a measure of ecclesiastical control. Human dissection,

for instance, was strictly supervised by the Church. Learning hadin Latin its own universal language. The system and content of

education in every school and university were so similar that a

scholar could find himself at home anywhere. In each the student

laboured upon the same texts, graduated by debating similar

philosophical themes, and (if he progressed as a man of learning)

SCIENCE IN 1500 3

found the stimulus to original thinking in problems familiar to all

men of education.

It would be mistaken to suppose that, because the intellectual

life of all Europe at the beginning of the sixteenth century was as

homogeneous as that of the modern nation state, it was character-

ized by a dull uniformity. There were, and there had long been,distinct and to some extent rival schools, just as there was also a

special development of some type of study at a particular place,

theology at Paris, law and medicine at Bologna and Padua. In

one place men still clung to the pure Aristotelean tradition, at

another they had begun to criticize it; here the Arabic physicianswere more highly regarded than the newer Greek texts, there theywere despised as poisoning the Galenic well of knowledge. Within

the acceptance of a common body of premisses there was vast

uncertainty concerning the way in which the premisses should

be applied. No one doubted that blood-letting was an essential

part of therapy: but there was great dispute over the actual tech-

nique. No one doubted that the world was round: but different

navigators could not agree on the best way to plot a course. Noone doubted that the calendar was out of joint: but the best

astronomers could not join in declaring the remedy. It is indeed

a misleading view of the early stages of the scientific revolution

to see them as involving only the conflict of two types of premiss,as typically in the antithesis between the Ptolemaic and the

Copernican world-systems. In fact much more was involved, the

practical and successful handling of detailed problems. This is

perhaps most clearly seen in the non-physical sciences, in anatomyor natural history in the sixteenth century, but it can also be seen

in the practical arts which depended upon the physical sciences.

Ultimately, of course, such an art (or science) as navigationadvanced very considerably through the substitution of the

L.opernican for the Ptolemaic astronomy; but in the sixteenth

century greater accuracy in cartography and oceanic navigationwas independent of the high truths of cosmology.The unity of learning which the sixteenth century inherited

from the middle ages is a strong mark of its diffusion. Scientific

knowledge in particular showed little differentiation in pattern,

though it varied greatly in quality and method, because it wasnot the native product of Christian civilization in Europe,but imposed upon it. The primitive Germanic tribes had long


submitted to a Romano-Hellenistic culture: first through their

contact with the Roman Empire, then through their conversion

to Christianity and the various efforts towards a renaissance of

learning that had followed; partly assimilated and legitimized

(as in witchcraft or folk-medicine), their original attitude to

Nature had largely sunk to the level of superstition in comparisonwith the "literary" science which won its supremacy in the

thirteenth century. As a first approximation, it may be said that

the cultural history of Europe, since the hegemony of the Roman

city-state, is mainly concerned with the diffusion of Hellenistic

influences, Greece itself being the heir to the ancient civilizations

of the Near East. Perhaps the nadir (by either political, economic

or intellectual standards) was reached about the sixth century;

by the ninth efforts were being made to assimilate the flotsam

surviving from the wreck of Roman Imperialism. Islam, em-

bracing many linguistic and ethnic elements, and having its

cultural focus in the eastern portion of the former Roman Empirewhich had been less devastated by popular movements than the

West, possessed greater potentialities for immediate development.The Arabic treatise on the astrolabe which Chaucer translated into

English c. 1390 had been written in the late eighth century; of the

Islamic medical authorities whom he mentions in the Prologue to

the Canterbury Tales, two had lived some four centuries before. In

the first phase of learning among Franks, Saxons and Lombards,science had been meagrely represented by a few Latin texts

fragments of Plato (the Tim<zus)> of Macrobius, and Pliny and

the degeneration of form and thought from these originals was

rapid. In the second phase, beginning early in the twelfth century,diffusion was concentrated into a very few channels, for the new

philosophical and scientific literature in Latin was created by its

very few scholars who were able to translate from Arabic, Hebrew,or more rarely directly from the Greek. The most famous of them,Gerard of Cremona (c. 1114-87) is credited with making at least

seventy translations, some of them like Avicenna's Canon, or

encyclopaedia, of medicine, of vast extent. Though the lists

certainly exaggerate the personal influence of one individual

upon the Latin corpus, it cannot be doubted that the somewhat

arbitrary selection exercised by a small group of linguists had a

determining effect upon the nature of the material available to the

purely Latin scholars of later generations. And it must be further

SCIENCE IN 1500 5

remembered that the Islamic and Hebrew scientific writings,

upon which the Latin translators worked, themselves representeda fraction accidentally or consciously chosen from the whole

original literature.

The intellectual life of medieval Europe was rapidly transformed

by this acquisition of a sophisticated method and doctrine in both

philosophy and science. Its influence can be traced in such varied

directions as the use of siege-engines in war, or the theory of

government, as well as in astronomy and physics. At first there

was opposition to the new type of study: the sources, being infidel,

were suspect, and they seemed to encourage a too presumptuous

inquiry into matters beyond human comprehension. But the

simplest Christian attitude, that men should not meditate uponthis world but the next, and that religion, rather than the works

of pagan philosophers, should instil the principles of moralityand ethics, had lost its force. The condemnation of the teachingof Aristotle's natural philosophy by a provincial council held at

Paris in 1210 proved ephemeral, as did later attempts to limit the

influence of Arabist sources. 1 Even before scholasticism developedthe study of Hellenistic philosophy upon Christian principles the

European mind was awake to the value of the riches laid before

it when refined from theological falsities. Robert Grosseteste

of Oxford in the first, and Thomas Aquinas in the second half

of the thirteenth century were the two foremost exponents of

Aristoteleanism, which as a method of reasoning and a fabric of

knowledge was thus reconciled with Catholic theology. Inevitablythe Hellenistic-Islamic renaissance of the twelfth century emergedwith an even greater homogeneity from this further process of

moulding. To the extent that Aristotle was seen through the eyesof St. Thomas and his influence was profound for it was he whomade Aristotle the master of medieval thinking the unity of

medieval culture was reinforced by the single Thomist tradition.

Averroism, the extreme rationalist appraisal of Aristotle's thought,became heresy. Despite Aquinas' deep study of every aspect of the

Aristotelean corpus, he utterly failed to understand the true spirit

and methods of natural science, 'and no scientific contribution

1George Sarton: Introduction to the History of Science (Baltimore, 1927-48),

vol. II, p. 568. A reputation for profound acquaintance with Arabic writings

was, however, long associated in the popular mind with skill in magical arts,so that a mass of legend was built up round such a figure as Michael Scot.


can be credited to him.' 1Against this dogmatic tradition, the

exponents of experiment (Grosseteste, Roger Bacon) and the

mechanistic school of critics (Jordanus Nemorarius, Jean Buridan,Nicole Oresme) of the same and later times were generally

unavailing, though they are interesting and important as the

precursors of the scientific revolution.

The time of maturation was really astonishingly short. It is a

common delusion that medieval intellectual life was stagnant over

the many centuries that separate the fall of Rome from the rise

ofFlorence. On a more just assessment the beginnings of intelligentcivilization in Europe may be placed no more than four hundred

years before the Italian renaissance: a longer interval separatesEinstein from Copernicus, than that which intervenes between

Copernicus and the earliest introduction of rational astronomy to

medieval Europe. Within a century of the first translations Latin

contributions to creative thinking were at least equal to those

made in any other region of the globe: by the mid-fourteenth

century the period of assimilation was over, the emphasis lay on

original development and criticism, and the initiative which it has

since retained had passed to the West. The renaissance pf the

twelfth and thirteenth centuries was imitative and synthetic; that

of the fourteenth was exploratory, critical, inquisitive. Authorship

began to pass from commentary to original composition, althoughstill often in the commentatory form. There are signs of true

science: the development of mathematics, now aided by the

"Arabic" numerals which were of Indian provenance; anatomical

research pursued in actual dissection; the development of a newmechanics employing non-Aristotelean principles and the rudi-

ments of a geometrical analysis. At the same time and there maybe^a correlation here which becomes more explicit and conscious

in the seventeenth century there was considerable technological

progress. The magnetic compass was first described in Europe byPeter the Stranger in 1269; gunpowder was applied to the propul-sion of projectiles about 1320; the third of the great medieval

inventions, printing, began its pre-history about 1400. But these

are only the most striking examples of a long series: the introduc-

tion, or wider exploitation of new materials like rag-paper, of

processes like distillation, of new machines like the windmill or

1George Sarton: Introduction to the History of Science (Baltimore, 1927-48),

vol. II, p. 914.

SCIENCE IN 1500 7

the mechanical clock, of new mechanical devices like the stern-

rudder for ships, or the use ofwater-power for industrial purposes.

Although philosophers and theologians still regarded slavery as a

justifiable social institution, the Latin 1 was the first civilization to

evolve without dependence upon servile labour. From the eleventh

century onwards the rigours of villeinage were mitigated andservitude disappeared. The phenomenon of the new social fabric

was, that while the general wealth increased, the inequalities in

its distribution tended to become more moderate. In fact the

fourteenth century shows the beginnings of a characteristic of

modern European civilization, the utilization of natural resources

through means progressively more complex, efficient andeconomical in the expenditure of human labour. These are the

first signs of an attitude to Nature, and to technological pro-

ficiency, which was to become overtly conscious in the writingsof Francis Bacon but was not to attain its fulfilment before the

nineteenth century. A manuscript of 1335, written by Guido da

Vigevano, a court physician who was no insignificant investi-

gator of human anatomy, already develops the application of

mechanical skills to the arts of war (in this instance a projectedcrusade to recover the Holy Land) in a manner typical of the

"practical science" of the Italian renaissance and later ages.

Again, it must be observed that few of the inventions mentionedabove originated in the Latin West. The common principles of

machine-construction were familiar to the later Hellenistic

mechanicians: other discoveries, like the compass and gunpowder,were transmitted to Europe from the Far East through Islam.

But it was Latin society which was transformed by them, not that

of Eastern peoples: and it was the Latins who, as in the realm of

ideas, alone fully realized and extended their possibilities. In the

end it was the West that rediscovered the East, arriving in the

ports and coasts of India and China with an admitted technical

and scientific superiority.

This is the background to what was once regarded without

qualification as"The Renaissance." The humanists of the six-

teenth century, who created the legend of Gothic barbarity,

1

Since, during the middle ages, not all Europeans were members of the

Roman Catholic, Latin-writing civilization, it seems convenient to adopt the

noun "Latins'* and the adjective "Latin" in a general sense as descriptive ofthose Europeans who were members of this civilization.


participated in a new phase of the diffusion of Hellenistic culture.

For them the past was not merely a store of knowledge to nourish

the mind, but a model to be directly imitated. Upon them, from

its newly discovered texts, and from its extant relics in Italy and

France, the pure light of the Hellenistic world seemed to shine

directly, and they disdained the reflected splendour of Islam.

Medieval scholarship seemed limited, obtuse, pedantic. It had

embroidered and perverted what it had not truly understood.

Through the perspective of the unhappy and generally, perhaps,

retrogressive fifteenth century, the whole medieval period was

seen in a jaundiced aspect. The decay of medieval society, and of

medieval intellectual traditions, produced a revulsion in the

minds of the first exponents of an art, literature and science which

were at once more authentically classical, and more modern.

The fathers of the Italian renaissance were Petrarch (1304-74)and Boccaccio (1313-75); they, with other originators of a new

literary and artistic movement, were contemporary with the heightof medieval science. To its exacting discipline and subtle ratio-

cination the new emphasis on taste, elegance and wit was by nomeans wholly friendly. In one important aspect the renaissance

was an academic revolt against the tyranny of expositors and

commentators, but the scholars who turned with renewedenthusiasm to original texts came close to surrendering somethingof value, namely the critical analysis and extension of Hellenistic

science due to generations of Islamic and Latin students of

philosophy and medicine. These gains, which the superior texts

of the scholar-scientists of the early sixteenth century would

hardly have recompensed, would have been sacrificed if the

renaissance had abandoned the middle ages as completely as the

academic revolutionaries wished; but such was not the case, andto a large extent the fourteenth century was assimilated by the

sixteenth.

As this suggests, there are important reservations to be made

concerning renaissance humanism as a force making for innova-

tion in science. For example, it can have had little impact uponthe early printers who published large numbers of medieval books,nor upon the readers who presumably desired them. And in their

revision of classical authors for the press the scholar-scientists wereif anything less prone to comment adversely upon them than their

medieval predecessors. Among the humanists intense admiration

SCIENCE IN 1500 9

for the work of antiquity led to the belief that human talent and

achievement had consistently deteriorated after the golden age of

Hellenistic civilization; that the upward ascent demanded imita-

tion of this remote past, rather than an adventure along strange

paths. Thus the boundary between scholarship and archaism was

indefinite, and too easily traversed. Some branches of science

were indeed directed to new ambitions, others were raised rapidlyto a new level of knowledge, but it cannot be said that all benefited

from a single influence favouring realism, or originality ofthought,or greater scepticism of authority. On the contrary, humanismsometimes made it more difficult to enunciate a new idea, or to

criticize the splendid inheritance from antiquity. Against the free

range of Leonardo's intellect, or the penetrating accuracy of

Vesalius' eye, must be set the conviction that Galen could not

err, or the view of Machiavelli that the art of war would be

technically advanced by a return to the tactics and weapons of

the Roman legion.

Obviously such rigid adherence to the fruits of humanistic

scholarship did not yield the renaissance of scientific activity

beginning in the late fifteenth century. Rather it sprang from the

fertile conjunction of elements in medieval science with others

derived from rediscovered antiquity. So in mathematics the

revelation of Greek achievements in geometry provoked emula-

tion, yet the algebraic branch of Islamic origin (for which

humanism did nothing) made equally rapid progress. Ultimatelythe union of the two effected a profound revolution. Moreover, to

take a more general point emphasized by Collingwood,1 the

renaissance attitude to natural events was so different from that

of the ancients that the classical revival inevitably led to someanomalous results. Thus one may account for the vast interest in

Lucretius' poetic statement of Greek atomism, De natura rerum,

rediscovered in 1417, and the eminence granted to Archimedesas the archetype of the physical scientist. Already in the fourteenth

century there were clear signs of an approach to a mechanistic

philosophy of nature, and the use of mathematical formulations,in the physical sciences where such a novel attitude could do muchto liberate the scientist from discussions of the metaphysics of

causation and to lead him to concentrate attention upon the

actual processes of natural phenomena. In this respect the broader1 The Idea of Nature (Oxford, 1945).

io THE SCIENTIFIC REVOLUTION

interests of humanistic scholarship reinforced a tendency which

they could not have initiated, a reaction against Aristotle. Althoughthe revival of Greek atomism had an important influence, the

"mechanical philosophy" of the seventeenth century representedmuch more than just this.

A more complete access to the works of Euclid, Archimedes

and Hero of Alexandria (among many others) gave a fertilizing

inspiration to physics and mathematics, but it was on the biological

sciences that the superior information of the ancients, resulting

from a more serious attention to observation, had its greatesteffect. Encyclopaedic study by medical men of the complete works

of Hippocrates and Galen, by naturalists of those of Aristotle,

Dioscorides and Theophrastus, played a large part in the scientific

endeavour of the sixteenth century, only slowly overshadowed by

original investigation. Even at the close of the century studies in

the structure, reproduction and classification of plants andanimals had barely surpassed the level attained by Aristotle.

Later still William Harvey could regard him as a principal

authority on embryological problems. Undoubtedly a return to

purer and more numerous sources of Greek science was a refresh-

ment and stimulus; despite the imperfections in the renaissance

scholar's appreciation of the immediate and the remote past, he

rightly felt that such sources laid before him new speculations,

facts and methods of procedure, suggested many long-forgotten

types of inquiry, and disclosed a wider horizon than that knownto the medieval philosopher. To a growing catholicity of interest

printing added the diffusion of knowledge. The tyranny of majorauthorities inherent in small libraries was broken for the scholar

who could indulge in an ease of compilation and cross-reference

formerly unthinkable. But it is not to be supposed that the methodof science, or the realization of the problems it was first to solve

successfully, were simply fruits of the renaissance intellect. Nascent

modern science was more than ancient science revived. Throughthe revived Hellenistic influence in the sixteenth century, always

diverting and sometimes dominating the development of scientific

activity, the strong current of tradition from the middle ages is

always to be discerned.

In 1500, when Leonardo da Vinci was somewhat past his prime,the scientific renaissance had hardly begun. Scientific humanism,

SCIENCE IN 1500 ii

the great critical editions, and the first synthetic achievements

under the new influences, were the work of the next generation.It was once usual to see such men as Nicholas of Cusa, Peurbach,and Regiomontanus in the fifteenth century as forerunners of a

scientific revival, but more recent estimates of their works serve

rather to emphasize the continuity of thought, than to indicate

an incipient break with the past. And though a vast volume of

medieval manuscript was left undisturbed and rapidly forgotten,

the larger proportion of the scientific books printed before 1500contained material which was familiar two centuries earlier. The

general stock of knowledge had hardly changed, as can be seen

from such a compilation as the Margarita Philosophica of GregoriusReisch (d. 1525), published in I5O3.

1 This was an attempt at an

encyclopaedic survey, perhaps rather conservative, certainly

immensely simplifying the best knowledge of the age, but useful

as a conspectus of scientific knowledge at the opening of the

sixteenth century. The pearls of philosophy are divided under nine

heads which treat of Grammar, Logic, Rhetoric, Arithmetic,Music (theoretical, i.e. acoustics, and practical), Geometry (pureand applied), Astronomy and Astrology, Natural Philosophy

(mechanics, physics, chemistry, biology, medicine, etc.), andMoral Philosophy. There is also (in the later editions) a Mathe-matical Appendix which deals with applied geometry and the

use of such instruments as the astrolabe and torquetum on which

medieval astronomy was founded. Reisch's design thus corre-

sponds closely to that of the typical arts course in the universities

of the period, which proceeded from the trivium (grammar,rhetoric and logic) to the quadrivium (arithmetic, geometry,

astronomy and music).

Astronomy^ was the most systematic ,ja, Uxa sciences^ The

phenomena of the heavens had long been subjected to mathe-

matical operations, though opinions differed on the most suitable

manner of applying them, and prediction of the future positionsof sun, moon and planets, the groundwork of astrology, was

possible to a limited degree of accuracy. Mathematical astronomyhad been advanced to an elaborate level by the Greeks, and still

further perfected by the mathematicians of Islam, who had also

been patient and accurate observers. For cosmology in the modern

1 At least nine editions were printed before 1550; others appeared as late as

1583 (Basel) and 1599-1600 (Venice).

ia THE SCIENTIFIC REVOLUTION

sense there was almost no necessity: the universe had been created

at a determined date in the past in the manner described in HolyWrit, and would cease at an undetermined but prophesied date

in the future. It could be proved, both by reason and by divine

authority, to be finite and immutable, save for the one speck at

the centre which was earth, unique, inconstant, alone capable of

the recurring cycle of growth and decay. As Man was the climax

of creation, so also the earth (though the most insignificant partof the whole in size) was the climax of the universe, the hub about

which all turned, and the reason for its existence. It was natural

for men who were unhesitant teleologists to believe that the

pattern of events was designed to suit their needs, to apportion

light and darkness, to mark the seasons, to give warning of God's

displeasure with his frail creation. In varying degrees of sophisti-

cation such an attitude is universal and primitive, and there maybe added to it that stage of astronomy, arising immensely later

in the history of civilization, when the alternations of the skies

are seen to be cyclic, and therefore calculable. But in the tradition

of astronomy which prevailed in 1 500 there was a third element,of purely Greek origin, which provided a physical doctrine

describing the nature of the mechanism bringing about the

appearances. The simple form of this mechanism to which the

Greeks were led by their reflection on the Babylonian knowledgeof the celestial motions was described by Aristotle; the complexform, capable of accounting for more involved planetary motions,was due to Ptolemy. The former was a physical rather than a

mathematical doctrine, the latter was mathematical rather than

physical, corresponding to what would now be described as a

scientific model of actuality.In a debased form, and strongly influenced by Platonic

hylozoism, the simpler Greek theory had never been entirely lost

to the middle ages. The translators brought Ptolemy's Almagestand many Arabic astronomical texts to Latin science An abstract

of spherical astronomy, which did not treat of the planetarymotions in detail, the Sphere of John of Holywood, became a

common text in the later middle ages and was printed thirty

times before 1500. The Margarita Philosophica describes the

"mechanism of the world" as consisting of eleven concentric

spheres; progressing outwards from the sublunary region with the

earth as the centre, they are those of the moon, Mercury, Venus,

SCIENCE IN 1500 13

the sun, Mars, Jupiter, Saturn, the Firmament (Fixed Stars),

the Crystalline Heaven, the Primum Mobile, and the EmpyraeanHeaven, "the abode of God and all the Elect." The spheres were

conceived as of equal thickness, and fitting together without

vacuities, so that for example the sphere of Saturn was im-

mediately adjacent to that of the fixed stars. Philosophers were

less clear on the physical matter of the spheres (Aristotle's perfect

quintessence as contrasted with the four mutable elements of the

sublunary world) apart from the fact that they were rigid and

transparent; having no dynamical theory they were not puzzled

by problems of friction, mass and inertia. The tenth sphere, the

Primum Mobile, which imparted motion to the whole system,

Devolved from cast to west in exactly twenty-four homes* The

eighth, bearing the fixed stars, had a slightly smaller velocity,

sufficient to account for the observed precession of the equinoxes.Between these the crystalline heaven was added to account for a

supposed variation in the rate of this precession. Then, descendingtowards the centre, as the spheres became slightly less perfect,

more sluggish and inert, each completed its revolution in a

slightly longer period, so that the sun required 24 hours 4 minutes

between two successive crossings of the meridian, and the moon

24 hours 50 minutes, approximately. This increasing retardation

resulted (as we now know) from a combination of the orbital

velocity of the earth and the orbital velocity of the planet; the

whole heavens revolved round the earth once in 24 hours, but the

sun, moon and planets appeared to move also in the oppositedirection at much smaller, and varying, velocities.

With these motions established, simple spherical astronomy was

taught just as it is today. But this simple theory did not allow of

prediction, it did not take into account the motion of the moon's

nodes, causing the cycle of eclipses, nor the variations in brightness

(i.e. distance) and velocity of the heavenly bodies. It is possibleto derive predictions from purely mathematical procedures, as

the Babylonians did, without making any hypothesis concerningthe mechanism involved. Till modern times the astronomer had

nothing to work with other than angles, angular velocities, and

apparent variations in diameter and brightness. He was unable to

plot the orbit of a planet in space: the best he could do was to

fabricate a system which would bring it to the proper point in the

zodiac at the right time. The Greeks, however, could not renounce


the system of homocentric spheres altogether, and their geo-

metrical methods based on the circle (in which, it was assumed,

motion was most perfect since it was perpetual and uniform)facilitated the construction of an analogous, but more complex,mechanical model. 1 As an example, the system of spheres whose

combined motions are responsible for the observed phenomena of

the planet Saturn is thus described by Reisch. It fills the depth,

represented by the seventh sphere in the simple theory, between

the interior surface ofthe sphere of fixed stars, and the exterior sur-

face of the sphere of Jupiter, both of which are exactly concentric

with the earth. Taking a

section through the Saturn-

ian spheres in the plane'

of the ecliptic, A (Fig. i)

is the outer surface of the

largest sphere, concentric

with the earth, B is its interior

surface which is eccentric.

C is a wholly eccentric

sphere, the deferent, carryingthe epicycle F embedded in

it. D is the outer surface of

the third and innermost

sphere, which is eccentric,

and E is its inner surface

which is concentric with theFIG. i . The Spheres of Saturn.

earth. Within E follow the remaining planetary systems of spheresin their proper order. The epicycle F, which actually carries the

planet Saturn, rolls between the concentric surfaces B and D.This is the mechanical model, which requires four spheres,

instead of one, to account for the motions of Saturn. The principlesof Aristotelean physics were observed, since the spheres by com-

pletely filling the volume between A and E admit no vacuum. Torepresent the phenomena accurately the astronomer had to assigndue sizes, and periods of revolution, to the various spheres, whichwere imagined to be perfectly transparent so that their solidity

1 Both the theories could be represented by actual models. Spherical astro-

nomy and the doctrine of multiple homocentric spheres was illustrated by the

Armillary Sphere, of which the Astrolabe is a plane stereographic projection, thePtolemaic theory of planetary motions by the Equatory or computer, whichseems to be a rather late development in both Islamic and Latin astronomy.

SCIENCE IN 1500 15

offered no obstruction to the passage of light to the earth. Thewhole system of Saturn (and of every other planet) participated in

the daily revolution from east to west; in addition the spheres ABand DE revolved in the opposite direction with a velocity of i 14'

in a century this corresponds to the slow rotation of the peri-helion of Saturn's orbit in modern astronomy. The deferent Ccarried round the epicycle in a period of about thirty years, but

its motion was not uniform with respect to its own centre P, or to

that of the earth O, but to a

third point Q, so placed that

OP = PQ, called the equant.

By this means the unequalmotion of the planet in its pathwas made to correspond more

closely with observation.

Finally, the epicycle itself re-

volved in a period of one year.The great virtue of the epicyclewhich was used by Hippar-

chus before Ptolemy was that

it enabled periodic fluctuations

in the planets' courses throughthe sky, the so-called "stations"

and "retrogressions" to be

represented (Fig. 2).

The epicycle was essentially

a geometrical device for' '

savingthe phenomena," and attemptsto make a physical reality of it

were late and unsatisfactory.

Epicyclic mechanisms similar

to that of Saturn were required for all the other members of the

solar system, except the sun itself. Those ofJupiter and Mars were

identical with that of Saturn, with appropriate changes in the

values assigned, while the mechanisms for the inferior planets,

Venus and Mercury, and for the moon, were more complex andinvolved a larger number of spheres.

1 In all, the machina mundi

1 There is an obvious and necessary relationship between the sizes and speedsof rotation assigned by Ptolemy to his circles, and those later adopted in the

Copernican system, but this relationship is not consistent. With Venus and

5-21

FIG. 2. The Geometry of the Epicycle

(Jupiter). E, Earth; J, Jupiter.The dotted line shows the approxi-mate path of the planet, whose"stations" occur about B and D,and whose "retrogressive'* motionis from D to B.

i6 THE SCIENTIFIC REVOLUTION

described in the Margarita Philosophica required 34 spheres, but at

various times much larger numbers had been used in the attemptto represent the phenomena more accurately. Oncjejhe .constants

of each portion of the mechanism had been determined in accord-

ance with observation, it was possible to draw up tables from

which the positions of the heavenly bodies against the backgroundof fixed stars in the zodiac could be calculated for any necessary

length of time. Unfortunafely it was well known by 1500 it was

a scandal to learning that calculations were not verified byobservation. Eclipses and conjunctions, matters of great astro-

logical significance, did not occur at the predicted moments. Themost notorious of astronomical errors was that of the calendar:

the equinoxes no longer occurred on the traditional days, and the

failure to celebrate religious festivals on the dates of the events

commemorated caused great concern. In fact the Julian calendar

assumed a length for the year (365^ days) which was about eleven

minutes too long: the necessary correction was adopted in RomanCatholic states in 1582. But at the beginning of the century the

causes of these errors in prediction were by no means clear. Thecurrent astronomical tables had been computed at the order of

King Alfonso the Wise of Castille at the end of the thirteenth

century and were out of date. Were the faults of the tables due to

the method by which they were prepared based on the Ptole-

maic system or were they due to the use of faulty observations in

the first place, the method being sound? The fact that Copernicus

Mercury Ptolemy's deferent represents the orbit of the earth in the Gopernicansystem, and the epicycle that of the planet. With the remaining planets

Ptolemy's deferent represents the orbit of the planet, and the epicycle that of

the earth.

The values of the Ptolemaic constants, and those of their modern equivalents,

may be compared thus:

Ratio of Radii Mean Distances

EpicycleIDeferent (in ast. units)

Mercury 0-375 : 1

Venus 0-719 : i

Earth

Deferent/EpicycleMars 1*519 i

Jupiter 5'2i8 i

Saturn 9 230 i

0-3870-723

i -ooo

1*5245-2039-539

Angular Velocities

(deg. per day)

of Epicycle

i 602 i 4

of Deferento 524060-083120-03349

Sidereal

Mean DailyMotion

4-09234i -60213

0-98561

0-52403o 08309*0-03346

SCIENCE IN 1500 17

chose the first alternative, that he accepted Ptolemy's observations

and rejected his mechanical system, was to be of great historical

significance.

It is important to realize and the problems became clearer

when the first Copernican tables came into use that the diffi-

culties were not merely conceptual. Suppose that the position of

Mars is to be predicted within an accuracy of one hour: then the

position given, and hence the original observations, must be accu-

rate to less than two minutes of arc, an accuracy quite beyondastronomical instruments before the invention of the telescope. Alarge astrolable, of one foot radius, for example, could not usefully

be divided to less than 5' intervals. For these reasons, certain

oriental observatories had erected huge gnomon-like instruments

in masonry to observe the motions of the sun with greater pre-

cision, and there was a somewhat similar trend towards increase

in scale in Europe during the fifteenth century. With these it was

found, however, that as scale increased new errors crept in, andthe estimated accuracy was not reached. Secondly, mathematical

procedures were highly involved. In the simplest case it was neces-

sary to establish (from the tables) the position of perigee in the

orbit, and then the place of the centre of the epicycle with respectto this. Then the rotation of the epicycle itself had to be taken into

account, and referred to the equarit. Finally the position as seen

from the equant point had to be recalculated as a position seen

from the earth. Real skill was required to compute a planetary

position with any accuracy from the tables, and very few even

in the sixteenth century could confidently undertake the task of

computing the tables themselves.

The earth, considering the relative potentialities of human

knowledge, was much less known than the skies, where the fixed

stars had already been plotted more accurately than any Europeancoastline. It was essential in the prevailing fabric of knowledgethat the mutable globe and the unchanging heaven be entirely

distinct. It was unthinkable that the same concepts of matter andmotion should be transferred from the sublunary to the celestial

region, and therefore all transient phenomena cometsa shooting

stars and new stars were regarded as mere disturbances in the

.upper region between the earth and the moon's sphere. This was,

indeed, the region of the element foe; below it the element air

formed a relative shallow layer above the surface of the globe. The


earth was composed predominantly of the remaining two ele-

ments, water and earth, but with air and fire as it were trapped in it,

so that"\vh'eh ah bpportunity for their release occurred they natur-

ally ascended upwards to their proper regions. Conversely, heavysubstances made largely of earth and water sought to descend as

far as possible towards the centre of the cosmos, where alone they

belonged, the water lying upon the earth. It was believed before

the age of geographical discovery that only a sort of imbalance

in the globe enabled a land-mass fit for human habitation to

emerge in the northern hemisphere.The categories of motion played an extremely important part

in pre-Newtonian science: even Galileo did not succeed in liber-

ating himself from them completely. JPerfej^j:j^ was

an unquestioned cosjnnqlogicaljgrinciple, which gave consistency to

the whole theory of astronomy. In the sublunary region natural

motion was invariably rectilinear: away from the earth's centre

in the case of the light elements, and towards it in the case of the

heavy. Since the centre of the earth was a fixed point of reference

the definition of these species of motion occasioned no philo-

sophical difficulties. The earth and its elements were unique, and

as a concept like"heaviness,

"having no relation to anything but

the sublunary region (to apply it elsewhere would be meaningless)could only refer to a body's tendency to move away from or

towards the centre of the earth, so also definitions like "up" and"down" could be quite unambiguous. Violent motion on the

other hand, that is raising that which is naturally heavy, or

lowering that which is naturally light, was unprivileged and could

occur in any direction. Force was required to effect these violent

movements, because they were opposed to the natural order of

the universe, just as force was required to withdraw a piston from

a closed cylinder because nature abhors a vacuum. As soon as

the effective or retaining force ceased, natural motions would

restore the status quo ante. This plausible, though limited, doctrine

was of great importance as the foundation of mechanics. Man was

the agent of the great number of violent motions, and one reason

why mechanics played a minor role in the tradition ofscience until

the sixteenth century was perhaps just this fact that so muchmechanical ingenuity was directed towards reversing the natural

order it did not contribute to the understanding of nature, but

violated it.

SCIENCE IN 1500 19

A corollary drawn from the classification of motion again

distinguished celestial from terrestrial science. Motion was the

ordinary state in the former, rest natural in the latter. Whereverthe notion of inertia has been perceived, however dimly, it has

been seen most clearly exemplified in the motions of the

heavenly bodies. While natural motion in the sublunary regionexists for Aristotle as a possibility, it is clearly exceptional, exceptin connection with the displacements effected by living agents.

In terrestrial mechanics, therefore, attention was most obviouslydrawn to the compulsive or violent motions brought about by the

action of a force, and the natural motions which follow afterwards

in reaction, e.g. the fall of a projectile. It was not difficult, once

the question ofmechanics was approached in this way, to conceive

of force as producing motion from the state of rest, and as the

invariable concomitant of violent motion. Within itself inert

matter could have no potentiality for any other than its propernatural movement: and though Aristotle never explicitly formu-

lates the proposition that the application of a constant force gives a

body a constant velocity, it is implied in the whole of pre-Galileanmechanics. The natural order could not be defied save at the cost

of expending some effort, any more than a weight could be

suspended without straining the rope by which it is hung. As

against this simple principle there was a whole category of

phenomena of motion that had to be treated as a special case, of

which the motion of projectiles was the leading instance.

Observation could not overlook the fact that no form of motion

ceases instantaneously. Effort is required to stop a boat under

way, or a rapidly revolved grindstone. What was the source of re-

sidual force which could impel an arrow for some hundreds of feet

after it had left its mover, the bow-string? The main Aristotelean

tradition pronounced that the force resided in the medium, air

or water, in which the motion took place, the medium beingas it were charged with a capability to move, though it did not

move itself. The medium, indeed, plays a most important part in

the Aristotelean theory of motion, for it is its resistance to move-ment which is overcome by the application of a constant force,

limiting the velocity which can be attained. If a vacuum in nature

were possible (and this Aristotle denied), a moving body could

attain an infinite velocity since there would be nothing to limit it.

In this special case, then, the medium.Jias_a dual function^jts


resistance brings the moving body to rest, but its charge of motion

prctoacTs^fie^'

eHect of the force has ceased.

This apparently contradictory dualism was severely criticized byphilosophers who otherwise worked within the general frameworkof Aristotelean science, and an alternative theory of motion was

put into a definitive, and to some extent mathematical, form in the

fourteenth century, principally by two masters of the Universityof Paris, Jean Buridan and Nicole Oresme. The principle they

adopted, but did not invent, was that though rest is the normal

state of matter, movement is a possible but unstable state. Theyillustrated this conception by analogy with heat: bodies are usuallyof the same temperature as their neighbourhood, but if they are

heated above that temperature, the unstable state is only graduallycorrected. A moving body acquired impetus, as a heated todyacc|uired KeaFJ~ahd neither wasted away immediately. The

impetus jaccjuiredjvvas the cause of the residual motion; and only

wRen^tHc store was cxfiaustccl did the body come to rest. 1

Although the idea of motion as a quality of matter was retro-

gressive, and the analogy with heat false, the development of the

mechanical theory of impetus is of outstanding importance in the

history of science. Impetus mechanics was not widely diffused, andthe line of investigators who continued discussion of its tenets

down to the sixteenth century was somewhat thin. It is not dis-

cussed in the Margarita Philosophica, but it was well known to

Leonardo da Vinci, Tartaglia, Cardano and other Italians of the

renaissance period. In its finished form it is absolutely a medieval

invention, which was never displaced by the Hellenistic revival.

The notion of impetus was not inspired by any new observations

or experiments, nor did it suggest any. The facts which it soughtto explain were exactly those already accounted for in the originalAristotelean theory. But it was the work of truly creative minds.

Before the idea of impetus could be useful, it enforced a revalua-

tion of ideas on the nature of motion and, still more important,of ideas on the natural order. Ideas of motion, even in Aristotelean

physics, and still more in that of Plato before him and somemedieval philosophers later, had been integrally woven into a

1 Part of the difficulty of the early mechanicians lay in the disentangling of

such concepts as motion, velocity, inertia, kinetic energy, just as much later

the physics of heat was obstructed until the concepts of temperature, heat,

entropy were defined.

SCIENCE IN 1500 21

fundamentally animistic philosophy of nature, to the extent that

in the extremest form motion and change were denied to matter

except in so far as it was pushed, pulled or altered by various ani-

mated agencies. The theory ofimpetus, attributing to inert matter

an intrinsic power to move, was a decisive step in the direction

of mechanism. In a sense it first conferred a true physical property

upon matter, qualifying it as more than mere stuff, the negation of

empty space. The impetus theory contained the first tentative

outlines of the explanation of all changes in nature in terms

solely of matter and motion which was to figure so prominentlyin the scientific philosophy of the seventeenth century. Indeed,both Buridan and Orcsme foicshadow the greatest triumph of

seventeenth-century mechanism, Newton's theory of universal

gravitation. Since the heavenly spheres were perfectly smoothand frictionless, moving upon each other without resistance andwithout effort, they saw that when the whole system had been set

in motion it would revolve as long as God willed, without its

being required that each sphere should be animated by a guiding

intelligence.1

Although medieval science was ignorant of dynamics in the

modern sense, discussions of motion and the displacement of

bodies form a very important element in its physical treatises.

The other branch of mechanics, statics, although it was of some

practical usefulness, remained in a very rudimentary condition

until the rediscovery ofArchimedes' work in the sixteenth century.His famous hydrostatical principle was known to the middle ages,

but even such an original and profound writer as Oresme failed

to apply it successfully as for instance in his explanation of the

fact that a given piece of wood may weigh more in air than

another of lead, and yet be lighter than the lead in water. 2 Eventhe theory of the lever and the balance was imperfectly appre-hended. In these suBjects the classical inheritance was weak; the

authority followed was Aristotle; and the medieval writers had

failed to develop an experimental tradition of their own.J[n optics

they had a much surerfo\^daj:ion^ in the original work of PtolemyanHTts^ ^tensiolP&y tHe Arab Ibn al-Haitham (Latine Alhazen,

1 A. D. Menut and A. J. Denomy: "Maistre Nicole Oresme, Le Livre duGiel et du Monde," Medieval Studies, vols. Ill, IV, V (1941-3), esp. IV, pp. 181

et seq.2

Ibid.) vol. V, pp. 213-14.


c. 965-1039). Alhazen had actually conducted experiments, andmade measurements, and in the West the experimental and geo-metrical study of optics was continued by such men as Robert

Grosseteste and Roger Bacon in the thirteenth century. Shortlyafter the latter's death a great advance wa macje in practical

optics- -witlx. the invention of spectacles. The magnification of

objects by lenses, unrecorded in antiquity, was known to Alhazen;their ophthalmic use brought the glass-grinder's craft into being.As a result the Margarita Philosophica, for example, offers a more

C.H.=CryttolHn Humour

FIG. 3. Section through the human eye, from the Margarita

Philosophica (translated). Nucaperforata Iris,Secundina= Choroid, Crystalline Humour= Lens, Spider's Web? Ciliary processes.

rational and complete account of the phenomena of light than of

any other part of physics though it is to be found under a dis-

cussion of the powers of the"sensitive soul" not in the section on

natural philosophy. Light is defined as a quality in the luminous

body having an intrinsic power of movement to the object, which

may be either the eye or an opaque body thus illuminated. Colours

are_somcwha^ sjmil^^ qualities in the

surfa(SLQfix&ii^ the incidence of light.

Next the structure of the eye is described, with the aid of a good

diagram of a section through the organ, and the functions of the

seven tunics and four humours are explained (Fig. 3). The opticnerve is said to conduct the

"visual spirit" to the brain, and single

SCIENCE IN 1500 23

vision with two eyes is simply accounted for by the union of the

two optic nerves into a single channel. The shining of rotten fish

or fireflies is attributed to the element of fire in the compositionof their substance. 1 Reflection and refraction are quite intelli-

gently treated. The fact that the ray of light passing from a rare

medium to a dense (as from air to water) is refracted towards the

perpendicular is explained by the greater difficulty of penetration.

Examples of the effects of refraction, such as the apparent bendingof a stick in water, are elucidated by simple geometrical figures,

and the apparent enlargement or diminution of the object seen in

accordance with the size of the visual angle at the eye is described.

In another section of the book the appearance of the rainbow is

explained: where tiny drops of water in the clouds are most dense

the sunlight is reflected as of a purple colour, where they are less

dense the colour is weaker and the light appears green, the

blue is the weakest of all. Refraction is not referred to in this

connection. Acoustics also was comparatively well under-

stood, both theorefically and experimentally. Reisch described

the physiology of the ear, the nature of sound as a vibration, andthe transmission of perception to the brain through the nerves

by means of an "auditory spirit." Music of course had its own

peculiar theory and practice, which are carefully outlined in the

Margarita.Other aspects of the knowledge of material things, which refer

rather to their composition, structure and generation than to the

phenomena which arise from motion of some kind, were broadlyrelated to the theory of matter derived froni AristPtlCi That all

substance accessible to human experience is composed of the four

elements, fire, air, water and earth, in varying proportions, seems

to have been a notion to which the earliest philosophers were

favourably disposed: it was accepted among the Greeks in pre-ference to the single-element theory of Thales, and very similar

ideas prevailed in China and India. It was not required that every

analysis should yield these elements in identical form, nor wasthere any means by which such an exact identity could have been

determined; but it is clear that the three ponderable elements

correspond roughly to the three states of matter (solid, liquid,

gaseous), with heat added as a material element. This conception

1Phosphorescence was studied with much interest in the later seventeenth

century, e.g. by Robert Boyle.


of heat (and electricity) as material though imponderable fluids

elements in fact if not in name had not become an anachronism

even by the end of the eighteenth century. A great deal of learningwas devoted to the question ofhow mixed bodies are compoundedfrom the elements, and how bodies generate by a synthesis of

elements, or corrupt by their dissolution. An important philo-

sophic problem was the relationship between the composition of

a substance and its qualities, or properties. Plato's doctrine of' c

essential forms?

' '

or ideal models, exercised its perniciousinfluence indirectly throughout the middle ages. Aristotle and

his followers believed that the elements themselves could be

transmuted from one to another, so that water could be condensed

into earth* or rarefied into air. Again, in a more strictly chemical

form, this conception lingered to the eighteenth century. The four

elements were of undefined figure, and matter was thought of as

being coiUinupus. Ancient atomistic speculation was known to

the middle ages through Aristotle's criticism of it, but that

criticism was regarded as wholly convincing. The conjunction of

elements in a compound body took place without any conceivable

hiatus or division; as Oresme says, they are not mingled like flour

and sand, for every fraction of the infinitely divisible compoundmust contain all its elementary constituents.

Regarding this framework of ideas from the point of view of

the chemist or mineralogist, its most important feature was the

latitude it offered for an infinite variety of theorizing on the

nature of change in substances. The only certain definition of a

substance J^a^jthat it must have form (i.e. fill some volume of

the universe) and substance (i.e. be material), and possess either

gravity or levity. FjDjrmjind substance are therefore in one sense

(as Oresme remarks) the first elements of matferj tTie four

elements proper have a secondary role and are transmutable.

Form likewise is obviously;.jnutabic : only substance could remain

constant; sinceitjsjdejrtru^^^ would require a change

injthe fixed finite volume of the universe. Consequently, what weshould now call physical or chemical changes could be accounted

for on any of three hypotheses: (i) variationTn tHejprojportibn of

elements, (2) the generation of elements (fire being the noblest in

the series}^ (3) the degeneration ofJthe elements. Ex nihilo nihilfit.

The first has in fact formed the main subject of chemistry, but

this limitation was only logically established by Lavoisier. In this

SCIENCE IN 1500 25

period the modern distinction between physical and chemical

changes would have had no meaning, since this differentiation of

properties was not yet established. The analogy, involved in the

use of such terms as"generation," between organic and inorganic

matter was consciously cultivated, being a natural product of the

animistic conception of nature. As the plant grows from earth and

water, so equally well could metals^ gems and stones.* In the

seventeenth century it was still believed that veins of ore would

grow in a mine if it was left to rest for a time unworked. And byvarious natural or artificial processes (the calcination of metals,the combustion of organic materials) one or more of the con-

stituents could be recovered. A vital principle, though of a

humbler kind, was just as much present in the sand which grewinto a pebble, as in the seed that grew into an oak. Natural historyhas only comparatively recently ceased to signify mineralogy as

well as biology, and the apprehension of the problems of formation

and change in the organic world as involving problems of a

different order from those encountered in the inorganic is a

comparatively late product of the scientific revolution. In so far

as it demands a differentiation between organic and inorganic

chemistry it was never appreciated by Robert Boyle. And it mustbe remembered that while it was possible to cite as examples of

matter "salt" or "flesh" without any doubt that the two were

precisely comparable, philosophy imposed an even higher degreeof theoretical unity. For the elements figuring in chemical changewere the elements of the sublunary world in cosmological

theory. The structure of explanation had to be consistent

between the macrocosm and the microcosm; the propertiesof "fire" or "air" as they were stated in the general pictureof the universe had to recur precisely when these elements

were considered as entering into the composition of organicmatter.

Closely allied to the theory of four elements was the. doctriiic of

the four primary qualities heat, cold, dryncss and humidity. Acombination of a pair

' of these qualities was[.attributed to eaclti ele-

ment, fire beingdry

and hot, air hot and moist, water moist and

cold, earth cold and dry, and Tfom mixtures of these elementary

qualities the secondary material qualities, hardness, softness, coarse-

ness, fineness, etc., were in turn derived, though other qualities1 But see below, p. 27.


colour, taste, smell, were regarded as intangible.1 Thus the

transmutation of elements was accomplished by successive stages.

through subsfitutiqn of qualities ;_ dried water becomes earth,

heated water becomes air, but to transform water to fire it must

be both heated and dried. It was reckoned that with each trans-

formation the volume was multiplied by ten, so that fire hadi / 1 ,oooth part of the density of earth. Meteorological phenomena,for instance, could be accounted for by the application of these

ideas in detail. The sun's heat turns water into air; the element

air, being light, rises; but high above earth (where it is cold) air is

transformed into water, and water being a heavy element falls

as rain. Similarly air in the caverns and cracks of hills is cooled till

it becomes water, which runs out as a spring. Comets are a hot,

fatty exhalation from the earth drawn into the upper air and there

ignited. The generation of" mixed substances" such as minerals

and metals in the interior of the earth under the action of celestial

heat from the primary elements and qualities was considered as a

more complex example of the same process. Stone is earth coagu-lated by moisture. Sal-ammoniac, vitriol and nitre are listed in the

Margarita "Philosophica as examples of salts formed from the coagu-lation of vapours in different proportions; to mercury, sulphur,

orpiment, arsenic etc. a similar origin is attributed. The metals

were commonly supposed to result directly from a combination

and decoction of mercury and sulphur though, as the alchemists

insisted, not the impure, earthy mercury and sulphur extracted

from mines and used in various chemical processes. Reisch, while

he admits the theoretical possibility of transmuting metals, pointsout the great difficulty of imitating the natural process of their

generation precisely, and seems doubtful of the pretensions of the

alchemists. Indeed, the ambition to tincture the base metals andotherwise modify their properties so that they should become in-

distinguishable from gold is far older than the Greek theory of

matter which gave it a rationale, and the actual processes or recipes1 The medieval theory of matter was derived mainly from Aristotle's

De Caelo (III, 3-8), De Generatione et Corruption (Bk. II), and Meteorologica.Cf. De Gen. et Corr., II, 3:

* hence it is evident that the "couplings'* of the

elementary bodies will be four: hot with dry and moist with hot, and againcold with dry and cold with moist. And these four couples have attachedthemselves to the apparently "simple" bodies (Fire, Air, Water and Earth) in a

manner consonant with theory. For Fire is hot and dry, whereas Air is hot andmoist (Air being a sort of aquaeous vapour) ;

and Water is cold and moist, whileEarth is cold and dry.*

SCIENCE IN 1500 27

traditional in the art of alchemy, some of which can be traced to

pre-Hellenic antiquity, had little reference to the philosophic idea

of metallic generation. But so long as the organic-inorganic analogyseemed plausible, alchemy could not be dismissed as mere folly.

As for the differentiation between the generation from the

elements of the world of inorganic substances like minerals, andthe generation of living organisms, it is obvious that this could

not be found merely in the principle of growth, or autogenous

development from a seed, for this was really common to both. It

could not be made material at all, and therefore the two broad

kinds of living nature^ were defined as possessing respectively a

vegetative and sensitive "Soul," man alone having in addition an

intellectual soul which gives him the power of reason. In membersof the vegetative class (plants) the organization of matter was

more subtle than in minerals: they were not passive creatures of

nature, like a stone, for they required to be supplied with water

and rich soil if they were to maintain their existence, they showed

cyclical variations, and they possessed special structures for repro-

ducing their own kind. The fixing of the margin of life is not

simple; our phrase "living rock" is the survival of an ancient

mode of thought, and the alchemists used to distinguish between

the "dead" metal extracted from the ore and the "live" metal in

the veins of the mine. But the need for nourishment, involvingsome process of "digestion," and the possession of a reproductive

system were recognized as distinctive of living creatures. It was

certain from theology that these had been created in the beginning,and perpetuated themselves without change ever since. The func-

UOJJL of the vcgctatiye soul was to control and indeed be the bio-

chemistry of the organism, t^whojte ^^ onlya part of the life: of the animal. For the animal is sensitive: it feels

pain, it is capable of movement, it can manifest its needs anddesires. Therefore it was endowed with a sensitive soul. Man has

vegetative soul, s^ a

and he alone

being endowed with the power of reflection, of detaching himself

from the mechanism of thc^body, was credited with_the_third,matter was everywhere the same, in rock,

in tree, or in dog, for it was well known that certain wells andcaves had the power of transmuting wood into stone, for instance:

the distinction between the animal, vegetable and mineral


kingdoms lay in the immaterial organizing principle which broughtthe elements into conjunction: nature could make pebbles growin streams, but not grass without seeds.

There was one important exception to this rule, founded (un-

fortunately) on the authority of Scripture and Aristotle alike.

A group of organisms, small as Aristotle originally conceived it,

obviously possessing the characteristics of life, seemed to have no

special mechanism of generation, but to develop directly from

decaying matten Some msects^ lichens^ mistletoe, maggots were

included in the class of spontaneously generated creatures which

had no specific descent, and to them the middle ages, from sheer

ignorance, added others such as the bee, the scorpion, and even

the frog. Once spontaneous generation had been admitted, it was

a fatally easy alternative to investigation, and the belief remained

unshaken till the mid-seventeenth century. Yet it was less anoma-lous than it might seem at first sight, for Aristotle was able to

imagine the circumstances in which spontaneous generation mightoccur after a fashion that corresponded closely with his ideas on

normal reproduction. Since the whole universe was in a sense, not

the full sense, animated, it was not illogical that some humble,borderline creatures should be born of it without parents.Of the excellent descriptive biology of Aristotle and Theo-

phrastus very little was known at the opening of the sixteenth

century. The middle ages had depended only too much on

compilers of the later Roman period and on fables both pagan andChristian. Such study was excluded from natural philosophy; it

might be just respectable as a form of general iknowledge, or

moral as it provided material to illustrate a sermon or emphasizethe minuteness of divine providence, but it offered none of the

sterner food for thought. Botanical or zoological curiosity is of

very recent origin; in most periods most men have been content

to acquire only the minimum of practical knowledge. A veryfew in the middle ages, like Albert the Great or the EmperorFrederick II, had an interest and attentiveness far above the

ordinary, but they founded no tradition. Observation was blunted,and it has been pointed out that naturalistic representation mustbe sought not in learned treatises, but in the works of craftsmen,

artists, wood-carvers and masons. Botany was cultivated to a

minor extent as a necessary adjunct to medicine and medieval

herb-gardens included both edible vegetables and medicinal

SCIENCE IN 1500 29

simples. In pharmacology native Germanic lore mingled with

the remnants of Hellenistic botany, so causing much confusion.

Plants named and described by the Greeks were identified with

the different species of western Europe; the nomenclature itself

varied widely from place to place; and there was no system bywhich one kind could be recognized with certainty from its

structure and appearance. As the quality of graphic illustration

and of verbal description deteriorated, the herbal became little

more than a collection ofsymbols, so that the mandrake which was

originally recognizable as a plant becomes a manikin with a tuft

sprouting from his head. Again, on the purely empirical side,

some progress was made in the selection of strains of corn, just as

it is certain that attention was given to the breeding of hawks and

hounds, but in none of these things was the plant or animal itself

the centre of interest. It existed simply to be cooked, or distilled,

or mutilated in man's service, or alternatively to play a part in

symbolisms of endless variety. There are, however, signs of a

more naturalistic outlook from the earliest beginnings of the

renaissance.

Natural history and scientific biology are both modern creations,

stimulated indeed by the rediscovery of Greek sources in the

sixteenth century. But this was not the only fruit of the Italian

renaissance, for naturalism is older in art than in science. It is

unnecessary here to discuss at length a change in the artist's spirit

and ambition which had such important consequences for biologyand medicine. It is at least fairly clear that the medieval draughts-man was not simply incapable of attaining realism, e.g. in matters

of perspective, but was not interested in perfecting direct repre-sentation. The element of symbolism was as important to him as

it has been in the twentieth century. No tradition of "photo-

graphic realism" existed which could serve the purposes ofscience,

such as was assiduously cultivated with the aid of perspective

instruments, camera lucida, and other devices from the seven-

teenth century to the perfection of photography, when art andscience again parted company. Partly under Hellenistic influence,

partly for internal reasons, art moved strongly in the direction

of realism and the faithful representation of nature in the fifteenth

century. Plants and animals became recognizable as individuals

rather than hieroglyphs. The tradition that artists should studythe anatomy of the animals and men they depict came into being,


reaching its peak in Leonardo da Vinci. This development was

powerfully reinforced in its scientific importance by the invention

of printing. Biology is peculiarly dependent upon graphic illus-

tration, and it is essential not merely that the illustration should

be accurate in the first place, but that it should be capable of being

reproduced faithfully. Nothing becomes corrupt more easily

than a picture or diagram repeatedly copied by hand; only a

mechanical process of reproduction, like the woodcut or the later

copper-plate, can maintain faithful accuracy. At the momentwhen the technique of visual representation was arousing greatinterest in the draughtsman and artist, printing made it possible

for illustrations to be copied in large numbers for teaching pur-

poses, so that the anatomical student and the botanist could

recognize the form of the organ or plant described in the text

when he saw it in the natural state.

The potentialities of the new interests and skills in biology

began to emerge only in the sixteenth century, as living creatures,

in their beauty, in the fascination of their habits, in the variety of

their species and ecological inter-relations, aroused a curiosity

and sentiment which has grown steadily in its extent throughoutthe modern period. The faithful imitation ofnature the necessaryformal basis of all naturalism was an aesthetic, rather than a

scientific revolution; the romantic nature-lover may not be a good

biologist. It was not until thought began to play upon the newfacts and the faults in the old traditions which passed for natural

history that precise observation could reveal consequences im-

portant for science, or that science could see in the flower not

simply an aesthetically pleasing object, or a symbol of God's

mysterious and benevolent ways, but a challenge to man's powersof understanding.

Science is an expanding framework of exploration, not the

cultivation of special techniques, or of a pecularly acute apprecia-tion of the wonder and unexpectedness of the universe in whichwe live. Medieval philosophers, who in this respect had a sharpsense of reality and a just notion of the importance of intellect,

had left natural history to such compilers as Bartholomew the

Englishman (c. 1220-40) whose book is an uncritical compendiumof classical fable and old wives' tale, flavoured with moralizations

and somewhat rarely enlivened by a touch of the countryman'slore. They judged that the typical was more significant than the

SCIENCE IN 1500 31

freak, unlike some of the scientists of the later seventeenth century

who, in misguided zeal for the principles of Francis Bacon, filled

the museum of the Royal Society with the heads of one-eyed

calves, internal calculi, an artificial basilisk. 1 None of the greatmen of the middle ages, with the exception of Albert the Great,showed more than a cool interest in natural history. As a result,

bestiaries, herbals and encyclopaedias were laborious summaries

of the bald notes available in classical sources, and none of themcarried more than the slightest indication of personal observation.

Heraldic beasts were listed with real animals; the legends of the

crocodile's tears, the pelican killing its brood and reviving themwith its blood, and the barnacle-goose born of rotten wood added

interest to the story: the lion and the fox became popular symbolsof bravery and cunning. Creatures were classified according to

the element in which they lived. The salamander was the onlyknown inhabitant of fire; birds belonged to air; fishes, whales,mermaids and hippopotami to water; and the rest to land. Trees

and herbs formed the two kinds of vegetable life, but only the few

species useful to man were noticed. Even common garden flowers

were ignored. Such work of compilation was regarded as a purely

literary task, and the authorities were quoted in wholly uncritical

fashion. Some scholars developed fantastic etymologies, such as

Neckham's Aurifrisius [Osprey] from"Aurum Frigidam sequens."

Roger Bacon pointed out the difficulty of interpreting satisfactorily

the more obscure names of creatures mentioned in the Bible

Biblical exegesis was one of the few respectable motives ibr

studying natural history at all.2 It scarcely existed save as an

appendix to some other branch of study. This is not really sur-

prising, since it is a trait of a sophisticated society to be interested

in things of apparently no concern to humanity. Natural philo-

sophy had for the middle ages an established place in the HouseofWisdom: natural history had yet to establish itself.

3

Francis Bacon wrote of scholastic philosophy that, from

immediate perceptions of nature, it*

takes a flight to the most

general axioms, and from these principles and their truth, settled

once for all, invents and judges of intermediate axioms.' Oncefundamental doctrines, the immovable earth, the four elements,

1 Cf. Nehemiah Grew: Musaum Regalis Societatis (London, 1681).2 G. E. Raven: English Naturalistsfrom Neckham to Ray (Cambridge, 1947).8 Cf. Appendix A.


or the souls of living organisms, are accepted as unshakablytrue, and explanations of the varied phenomena of nature

deduced from them, it is an inescapable consequence that the

structure of scientific knowledge has great cohesion, a logical

unity imposed from above. An empirical science, a science whichsees itself as unfinished and progressive, can tolerate inconsisten-

cies it is for the future to resolve them by some higher-order

generalization. Physicists might have debated for a hundred

years whether light is undulatory or corpuscular in nature, but

the progress of optics did not wait upon a resolution of the argu-ment. And while it is far from being true that medieval science

was exclusively deductive or exclusively speculative in everydetailed consideration of a particular phenomenon, it is true that

its structure was of the form that Bacon described. The character

of the structure is not changed by the fact that some philosophersmade a few experiments. The structure of modern physics is still

experimental, though some physicists do not make experiments.The difference is that the theoretical physicist bases his calcula-

tions upon materials obtained by the researches ofan experimental

physicist and produces a result which is itself capable of confir-

mation by experiment, whereas the medieval philosopher fitted

the results of his experiments into a theory already firm in his

mind. He knew what "light" was before making experiments on

refraction: he knew the cosmological significance of "weight"before attempting to determine the speeds at which heavy bodies

fall. Experiment and induction could only modify the minutiae

of science, and these (for example, the numerical values of astro-

nomical constants) were indeed frequently changed in the later

middle ages in accordance with experience. They could not

reflect upon the broad lines of the structure. It might indeed have

happened that Aristotelean science would have been crushed

under the accumulated weight of an adverse mass of experimental

testimony. But modern science did not in fact arise in this way.This too has its unity, of course a unity derived not from

deduction but from the homogeneity of its procedure and the

wonderful, unforeseeable interlocking of its branches over three

hundred years. Modern science, like medieval science, embraces

in this unity statements of fact, concepts and theories. It could

not function if it were not free to employ terms like "electron"

or "evolution," which are not applicable to crude facts, just as the

SCIENCE IN 1500 33

medieval philosopher could not think about plant-life without

introducing the entity"vegetable soul/' Within its own context

of theory the vegetable soul is not less plausible than the electron,

and it cannot be said that one or the other can be disposed of

by a straightforward matter-of-fact test. To do so it would be

necessary to make a complicated inquiry into the value of the

factual information supplied by observation and experiment, to

examine the reasoning involved in either case, to trace the rela-

tionship between the concept and other elements in the fabric of

science, and so forth, and it is because modern science in all such

activities differs from medieval that its fruits are different. Fromsuch intellectual activities modern science yields a system of ideas,

not an unlinked series of factual statements, being in this respect

(despite the immense superiority of its factual content) comparableto medieval science. And the latter, as a system of ideas, with all

the imperfection of its methods and information, was true science.

1 1 offered a^systcjn of explanationA closely related to the facts of

experience and satisfactory to those who used it, giving them a

degree of control over their natural resources and allowing themto make certain predictions about the course of future events. Bythese stanHards it was relatively vastly inferior to modern science,

just as at each stage in its own development modern science has

been inferior to the science of later stages. But to declare that anyof its tenets was unscientific is to misuse language. Unscientific

is a pejorative term meaning inconsistent with the prevailingframework of the explanation of natural events and the methodsused to establish this framework; it can have no other meaningbecause we do not know that what is scientific now will not be

unscientific in the future. There is no absolute standard. All that

can rightly be said, when we have understood that medieval menhad prejudices, purposes and hopes totally different from our

own, is that they were less inquisitive and self-critical than they

might have been. They were less interested in natural philosophy,for to them it was but a step forward to higher things. Science wasa means, not an end.

CHAPTER II

NEW CURRENTS IN THESIXTEENTH CENTURY

The subtlety of nature greatly exceeds that of sense and

understanding; so that those fine meditations, speculationsand fabrications of mankind are unsound, but there is no one

to stand by and point it out. And just as the sciences we nowhave are useless for making discoveries of practical use, so the

present logic is useless for the discovery of the sciences. 1

IN

such terms Francis Bacon, in the early seventeenth century,denounced the existing structure of scientific knowledge as he

knew it. Yet it is clear that the same structure of science hadsatisfied the many medieval philosophers of genius who had ex-

pounded it; even those who criticized the learning of their day,like Roger Bacon, could not depart from its strategic concepts.

Clearly the difference between the men who taught the Aristo-

telean world-system and those who later rejected it was not simplyone of intellectual calibre. Only when the criteria of what consti-

tutes a satisfactory scientific explanation changed, and when fresh

demands were made for the practical application of nature's

hidden powers, could an effective scepticism concerning the

strategic concepts take shape, as distinct from differences of

opinion on matters of detail. 2 When such scepticism arose the

cohesive strength of the science that prevailed in 1500, and on the

whole throughout the sixteenth century, became significant.

In modern science the higher-order generalizations are vulner-

able, but in descending the scale to the substratum of experimentalfact the chances of serious error steadily diminish. In Aristotelean

science the reverse was true: an important dogma, such as the

stability of the earth, might be incapable of experimental proof

1 Novum Organwn, Bk. I, x, xi.2 An important change also took place in the idea of hidden powers, as the

ambition to force "unnatural" operations on nature by esoteric or magicalmeans gave way to the belief that man could use processes as yet unknown butstill strictly rational or mechanistic.

34

NEW CURRENTS IN THE SIXTEENTH CENTURY 35

or disproof (as Galileo himself confessed), but some of the primary

propositions for example that bodies fall at speeds proportionalto their weights could be exposed as contrary to experience byvery simple tests. To modify the accepted scientific opinion of the

present time it is usually essential to carry out an intricate investi-

gation verging on the frontiers of knowledge; in attacking the

conventional science of the sixteenth century it was possible to

outflank: the:

B higher-order generalizations altogether by showingthat the

^'facts" deduced from them were simply not true. It

could not be a fundamental requirement of the world-order that

changes do not happen in the heavens if the new star of 1572 could

be shown to be far beyond the sphere of the moon by its lack of

parallax. This feature in the structure of Aristotelean science de-

termined a large part of the tactics of the scientific revolution.

Further, since the unity and cohesion of science were imposedfrom above, growing out of its majestic axiomatic truths, it fol-

lowed that when the results of any one chain of ratiocination were

impugned the shock was reflected in similar dependent chains.

Once it was known that the liver is not the source of the blood-

stream the whole physiology based on this belief was disposed of

at one stroke. Admittedly the iconoclasts were not always quickto recognize the necessary extent of their destructive criticism

least of all a Copernicus or a Vesalius which was often jubilantly

pointed out by their opponents. The weakness of conventional

science was also its strength; the whole authority of the magnifi-cent interlocking system of thought bore down upon an assault at

any one point. How could a mere mathematician assert the earth's

motion when a moving earth was absolutely incompatible, not

only with sound astronomical doctrine, but with the whole

established body of natural philosophy? Logically, to doubt

Aristotle on one issue was to doubt him on all, and consequentlysome problems of the scientific revolution, which may now seemto involve no more than the substitution ofone kind of explanationfor another, were pregnant with consequence since they impliedthe annihilation of extant learning.The sixteenth century shows the tactics of the scientific revolu-

tion in two contrasted forms. In the year 1543 were published two

volumes which have become classics of the history of science, the

De Humani Corporis Fabrica of Andreas Vesalius (1514-64) and the

De Revolutionibus Orbium Coelestium of Nicholas Copernicus (1473-


1543). Neither of these books was "modern" in content Yesalius

more,,succ.cssful._,_

in escaping the Hmitations_oL Galenic_ __

physiology than Copernicus in departing from the formal systemof perfect ckcks but both inspired trains of activity which were

to lead to the substitution of other conceptions for their own within

two generations. The two books and their authors, however alike

in their broad impact upon the scientific movement, are totally

dissimilar. On the Fabric of the Human Body is a work of descriptive

reporting; its value depends upon the trained eye of a greatanatomist and the skill of draughtsman and block-maker, while

Copernicus' treatise is purely theoretical. Vesalius was a youngman whose work, if it was his unaided, shows astonishing pre-

cocity. Copernicus was a dying man, of recognized capacity, whohad nursed his idea for thirty years. Vesalius* material was taken

freshly from the dissecting-table; Copernicus' was the laborious

digestion of ancient observations. Vesalius was an ambitious and

popular teacher who contributed to the fame of Padua as a centre

for the teaching of medicine which lasted till the mid-seventeenth

century; Copernicus lived obscurely immersed in his ecclesiastical

administration, hesitant to the last over the enunciation of his

great hypothesis. The nature of Copernicus' original contribution

to science is also quite different from that of Vesalius. The former

was the avowed opponent of an idea, that the earth is the motion-

less core of the universe, but his opposition rested in no way uponhis discoveries in practical astronomy, which were negligible, or

on the precision of his measurements, which was not remarkable.

It sprang from a demonstrable truth, that celestial observations

could be equally well accounted for if the earth and planets were

assumed to move about a fixed sun, allied to various wholly non-

demonstrable considerations value-judgments seeming to showthat the astronomical system constructed upon this assumptionwas simpler than the older system and preferable to it. Copernicuscriticized the internal logic of prevailing ideas, but to be a Coper-nican did not add one item to a man's factual knowledge of the

heavens, whereas it did place him in a position which could be

challenged on other grounds. Vesalius, on the other hand, gavevent to no formidably unorthodox opinions, rather indeed his

passing comments seem to condemn such innovations. ReveringGalen as the great master of anatomy, devoting his energies to

editions of Galen's works, it was with reluctance that Vesalius


differed from him. Neither theorist nor philosopher, his book

vastly enhanced the range and precision of knowledge concerningthe structure of the body, an essential foundation for the rational

physiology of which he had himself no prevision. In general his

medical thinking was quite traditional, only his view of what an

anatomical textbook should be provoked controversy. The publi-cation of Harvey's discovery of the circulation of the blood in

1628 aroused the first serious conflict between ancient and modernmedical theories. Yet it may be said that the beginnings of the

scientific revolution are to be found as truly in De Fabrica, and the

series of illustrated anatomies of which it was the outstanding

member, as in De Revolutionibus. As examples of types of innovation

they are complementary.The twin advance upon the distinct lines of conceptualization

and factual discovery constantly occurs in science. The former

makes the more interesting history, but it must not be forgottenthat each new observation, each quantitative determination

accurately made, is adding to the stock of knowledge and playingits part in the genesis of a new idea. Indeed, conceptualization can

only progress and rise above the level of speculation through the

accumulation of fact by the perfection of techniques of experi-ment and observation. Anatomy is the crucial instance of this

during the early period of the scientific revolution.

In the middle ages it is difficult to distinguish specialized medi-

cal sciences from the general practice of the physician and surgeon.There was a research interest of a sort in natural philosophy, even

though the research was of a peculiarly narrow kind and its sole

instrument formal logic. The medical sciences were even more

strongly subject to the limitations of the purpose for which theywere cultivated, the training of medical men. Yet some medieval

anatomists were imbued with a disinterested love of knowledge, a

trait which seems to have been stronger in the fourteenth centurythan it was about 1500. The tradition in medicine was at least as

tightly unified as that in natural philosophy. The principal auth-

ority in anatomy, physiology and therapy until the seventeenth

century was well advanced was that of Galen (A.D. 129-99).Other writers on medical subjects were of course studied: in

clinical matters great respect was accorded to Hippocrates, whoseworks were made more fully known by the humanists. Aristotle

was also followed in these subjects, sometimes in preference to


Galen, but it is not easy to overestimate the latter's power. Ahumanist physician, Dr. John Caius, as President of the College

of Physicians, could order the imprisonment, until he recanted, of

a young Oxford doctor who was reported as saying that Galen

had made mistakes. When men were educated as logicians andnot as observers it was infinitely easier to detect errors in philo-

sophy than in anatomy or physiology. Admiration for Galen wasso extravagant that anatomists were more apt to attribute their

failure to confirm his descriptions to their own want of skill, than

to his.'

I cannot sufficiently marvel at my own stupidity/ wrote

Vesalius, 'I who have so laboured in my love for Galen that I

have never demonstrated the human head without that of a lambor ox, to show in the latter what I could not find in the former.'

It was only tardily, and hesitantly, that Vesalius admitted to him-

self the simple truth that the structure then called the rete mirabile,

described by Galen in the human head, was a feature not of

human, but ofanimal anatomy.1Only gradually could anatomists

learn to see the body otherwise than as Galen had taught them,and the broader influence of his pathology lingered well into the

nineteenth century. Galen was one of the greatest medical scien-

tistswho have ever lived, demonstrating in Rome, some six hundred

years after Aristotle, the vigour and quality of Hellenistic science.

He dissected, he experimented and his work, though dominated bythe vitalistic preconceptions of Aristotle, has a strong experientialfoundation. He was also an uncritical teleologist, believing that

it is possible to discover the purpose of every part of the body andto prove that it could not be more perfectly designed for that

purpose. This profound admiration for the divine plan recom-

mended him strongly to Christian writers of the middle ages.

In many ways Galen epitomizes the typical qualities of the

Greek tradition in medieval science, itself often far superior to the

independent efforts of the later Latins, but so far imperfect that

even when it was purified and enriched by renaissance scholars

a reaction against it was still necessary before modern science

could take shape. Insome aspects the Greek intellectwas "modern" ;

but not in relation to medical subjects. Greek medicine never de-

tached itself from teleological arguments, and its anatomy was

1 De Fabrica (1543), p. 642. Quoted by Charles Singer and G. Rabin: APrelude to Modern Science (Cambridge, 1946), p. xliv. Doubts on this point hadbeen expressed earlier by Berengario da Carpi.


always firmly subject to a priori physiological theories, not lendingitself to the reverse and correct process. There was a deep-seated

prejudice against human dissection. As a result the study ofanimal

anatomy without sufficient check introduced numerous errors.

Galen worked extensively on the Barbary ape, he may possiblyhave had access to the still-born foetus, but he never dissected an

adult human subject. This lack ofexperience was scarcely appreci-ated before the time of Vesalius. Technical nomenclature andclassification were very defective in Greek anatomy, and even had

description been perfect it would have been useless to a later agein the absence of pictorial illustration. At its best the eye of the

Greek anatomist had often been deceived by his preconceivednotions of the working of the body. As in astronomy, the Greeks

had gone far in the direction of precise and careful research, muchof which proved of enduring value, but the observations theymade were fitted into a scheme of ideas inherited from primitivetimes.

The influence of Greek texts upon Islamic physicians hadbecome considerable by the ninth century A.D., when there was

much activity in translation. Avicenna (980-1037), the greatestscientist of the Arab world and its foremost physician, reproducedin his Canon the best features of a Hellenized survey of medicine, as

well as original observation. To some extent, with its importantdebt to Galen, the Canon replaced Galen's own writings, even in

the West. Gerard of Cremona in the twelfth century translated it

and a large part of the Galenic corpus, but not Galen's chief

anatomical works which were only Latinized in the fourteenth

century. Other Galenic texts were translated direct from the

Greek by William of Moerbeke, half a century later than Gerard.

Eventually, too, all the more important works in Arabic onmedicine became available, including the Kitab of al-Razi

(c. 850-924), an even larger encyclopaedia than Avicenna's Canon.

Before the sixteenth century the Islamic commentaries upon andadditions to the Greek originals had a decisive influence uponthe European knowledge of Hellenistic medicine.

Human dissection was discouraged in Islam. In Europe the

systematic study of anatomy seems to have begun in the twelfth

century, contemporaneously with the rise of the famous medical

school of Salerno, though the practice of actual dissection was a

north Italian development. The reception of Aristotle's writings


in the thirteenth century, temporarily interrupting the growth of

a purely Galenic anatomy and physiology, was counter-balanced

by a stronger interest in dissection, flourishing under the wider

privileges of the universities. Dissection was given countenance,

partly by the needs of surgery, and partly by legal recognition

(under the influence of the law-school of Bologna) of the value of

forensic evidence derived from the post-mortem opening of the

body. There has been at all times and in all places a universal

revulsion against the dissection of the dead to serve mere curiosity,

and perhaps it was not extraordinarily strong in the middle ages.

At least it is likely that human dissection was comparativelycom-mon at Bologna by the early fourteenth century, the legal post-

mortem having been transformed into a means of instructingstudents. Henri de Mondeville, in teaching anatomy at Mont-

pellier in 1304, illustrated his lectures with diagrams probably

copied from those used in the school at Bologna.1

Shortly afterwards, in Mondino dei Luzzi (c. 1275-1326),medieval anatomy reached its zenith. He dissected for research,

and he was probably the first teacher since the third century B.C.

to demonstrate publicly on the human body. His Anathomia, which

was printed many times, long remained a popular text. Eagerto reconcile authorities, he did not venture to assert his own views,

and perpetuated many mistakes. Good anatomists succeeded

Mondino (though none escaped his influence) but there was a

general deterioration in the teaching of the subject. Mondino had

expounded while at work upon the body; the standard practiceof a later age is familiar from a number of wood-cuts in early

printed books. The professor sat in his lofty chair, reading and

enlarging upon the Galenic text, while an ostemor directed the

operations of the humble demonstrator who wielded the knife. The

body again became merely an illustration to the words of nobler

men. Anatomy degenerated into the repetition of phrases andnames. No example of the misleading perspective adopted by the

renaissance scholar could be clearer than this: because he knewthat the teaching of anatomy had become a literary exercise in

the fifteenth century, he assumed that it had never been anythingelse, and that the only course was to return directly to the works

of Galen.

The curve moves upwards again towards the end of the fifteenth

1 Charles Singer: The Evolution ofAnatomy (London, 1925), p. 73.


century. One factor in this seems to have been pressure in the

medical schools for more demonstrative teaching; attendance at

dissections had to be restricted so that all might share in the

spectacle.1 Another was the official recognition of human dissec-

tion, under clerical licence, by the Papacy. The first printedanatomies with figures appeared in the last decade of the centuryand the first half of the sixteenth shows a whole group of able

practical anatomists at work Berengario da Carpi, Johannes

Dryander, Charles Estienne, Canano of Ferrara, Massa, in

addition to Vesalius. The humanists applied themselves to the

editing of famous medical texts, and others but recently recovered,such" as the De re medica of Celsus (first century B.C.), which

supplemented the medieval corpus. There was a powerful reaction

against the Arabic authorities, and the Arabic technical nomen-clature was gradually replaced by the classical terminology whichhas established itself. Galen's texts were studied in the original

Greek, and re-translated into Latin. English scholars under the

patronage of Reginald Pole had a large share in the edition of

Galen's Opera Omnia printed at Venice in 1525 the connection

between medicine and philosophy was rediscovered. 2 But scholars

were not practical anatomists, their enthusiasm reinforced, rather

than weakened, the medieval attitude to anatomical study. The

pure Galen still held all Galen's faults, for scholarship could

purify a text without touching on the errors in observation held

within it.

Another and more important source of inspiration was of a

different kind, the naturalistic movement in art which has alreadybeen mentioned. Italian artists had been engaged in the study of

anatomy well before the end of the fifteenth century, and from

surviving sketches by, for example, Michelangelo or Raphael, it

appears that they occasionally practised illicit dissection. Leonardoda Vinci (1452-1519) certainly did so as his interest in the fabric

of the body developed from his first attempts to analyse the

structure of the forms he was portraying. Some of the printedanatomical figures of the next generation are indeed reminiscent

of Leonardo's famous drawings. The representation of anatomical

structures as seen with the artist's eye and recorded by the artist's

1 Lynn Thorndike: Science and Thought in the Fifteenth Century (New York,1929)* P- 69, n. 22.

2 W. G. Zreveld: Foundations of Tudor Policy (Harvard, 1948), pp. 53-5.


pencil, which is totally different from the schematized, diagram-matic illustration of an earlier epoch, and even from the merelyworkmanlike but biologically accurate sketches oflater professional

anatomists, thus preceded the work of the founders of modern

anatomy. The means for duplicating such drawings alreadyexisted in the technique of wood-cut printing. From this source

the sense of the actual, of the minute, penetrated into academic

anatomy and it is significant that the artists were men who hadno stake in existing theory, and who, in the case of Leonardo at

least, were unschooled in the textual description of organs. But

there are limitations to the artistic impulse and to the naturalism

which is only interested in superficial forms. The artist's drawing

may not be most suitable for the purposes of a text-book; he needs

to know something of the configuration and function of the surface

musculature, of the run of the visible blood-vessels, and perhaps

something ofosteology, but he does not normally need to penetrateto the internal organs or the recesses of the skull. The artist at

the dissecting table would certainly seek to re-create the appear-ance of the living body from the structure of the dead but he

would not usually be interested in the correlation of function andthe ordering of parts which ultimately lead to the discovery of

physiological processes. Only when naturalism serves an impulsewhich is no longer purely artistic and has become the instrument

ofscientific curiosity can it have significance for medical anatomy.Of course it is abundantly clear that the motive which directed

Leonardo to make his perceptive and accurate sketches, to take

casts and prepare specimens by the injection of wax, was of a

truly scientific order. In him, as in Vesalius, artistic imaginationwas the servant of science. Yet some even of the most naturalistic

of Leonardo's drawings contain ., ancient errors, pjerhaps copiedfrom the vernacular anatomical text-books which were alreadyavailable to him: and to the organization of anatomy as a disci-

pline Leonardo, who had no talent for classification and arrange-

ment, contributed nothing. In any case the influence of his

crowded and ill-ordered note-books upon contemporaries is in

all respects entirely conjectural.If the historical situation were that teachers of anatomy and

medicine in the universities of France and Italy became them-

selves the pupils of professional artists unlearned in Galen it wouldbe unique and surprising. But this was not the situation. It was


rather that the work of the anatomist reflected, with less artistic

merit, the same general cultural trend towards naturalism whichaffected purely aesthetic representation more profoundly; and that

the anatomist made use of the same techniques of draughtsman-

ship and reproduction as the artist, whose stylistic conventions

were impressed upon his illustrations. Naturalism, and the desire

to take advantage of the new faculty of the wood-cut print for

exposition, forced him along the road to observation. Ifthe teacher

of anatomy wished to elucidate the Galenic account of the struc-

ture of the human body by pictures of the features described he

could do so only by dissecting a body and having drawings madehe could not reconstruct a picture entirely from a verbal text,

though the text might influence the instructions he would giveto the draughtsman. As, in so doing, anatomists observed dis-

crepancies between the text and the structures themselves they

departed with greater confidence from the Galenic model andlearnt to rely on observation alone. A few conservative anatomists

were well aware of the danger of illustrated texts; too great a

reliance upon visual images might lead to contempt for Galen's

superior knowledge. So in fact it happened that Vesalius' cuts are

sometimes less traditional and more accurate than his text. The

practice of making realistic not necessarily aesthetically pleasing

drawings elevated instructional dissection to the level of re-

search, but in the circumstances of the time opportunities for

making a recordable dissection were few and hurried. The ambi-

tion to make (for example) an accurate map of the venous systemneed not be taken to be ipso facto evidence of a critical spirit,

though it may indicate a more sensitive professional conscience.

As the first men to embark on such tasks were firmly convinced of

Galen's rectitude, there was no reason why they should not take

the liberty to draw what he had already perfectly described. It

was thus with Vesalius himself: not until his preparatory workfor the De Fabrica was well advanced did he realize the extent

to which Galen had transferred animal structures into human

anatomy. This misleading practice, and Galen's specific mistakes,

could not be exposed without an impulse to research which in fact

arose out of the needs of teaching and illustration. The errors in

text-book anatomy could not be discovered through a desire to

amend Galen by reference to nature because no one as yetbelieved this to be necessary.


All this has little relation, directly, to aesthetics. The first illus-

trated anatomies were not indeed beautiful books, though theycontained many new discoveries. It may well be that Vesalius'

superbly produced folio cast an undeserved shadow upon the less

splendid efforts of his contemporaries and immediate predecessors.

Perhaps too much emphasis has been placed upon its interest as

an example of the profitable co-operation between scientist andartist in the sixteenth century; certainly Vesalius

5

figures were fine

enough to prompt frequent plagiarism. The preparation of illus-

trated anatomies demanded such a collaboration, and providedan incentive for an original research, but Vesalius was not the first

to attempt a complete pictorial survey }which he began with

youthful energy. When in 1537 he set to work on De Fabrica, andcommenced teaching anatomy at Padua, Vesalius was twenty-

three. He could hardly claim to write with mature knowledge,and though he had studied medicine at Louvain and Paris, so far

as is known his experience of dissection was still very limited. Norwas he qualified to stand as an arbiter between Galen and Nature,for at Paris especially, under medical humanists who were un-

shaken followers of Galen, he had been well grounded in the

renewed Greek tradition. Vesalius' first notable publication wasa revision of Johann Gtinther's Anatomical Institutions according to

Galen (1538), and his second, the Tabula Sex, was a series of wood-cuts to illustrate the Galenic exposition ofhuman anatomy which,

though based on dissection, was still traditional in character and

repeated many ancient mistakes. It was not, apparently, until the

preparation ofDe Fabrica was well advanced (about 1539-40) that

Vesalius began to doubt whether an anatomy founded on natural-

istic illustration could be reconciled with Galen's descriptions.Even of Vesalius' finished work it has been said that: 'A few of

his comments reveal an active dissector less experienced than

his contemporaries Berengario da Carpi, Massa and Charles

Estienne.' 1

Creative scientific ability may run strongly in the direction

either of practical work or of theory. To the former talent the

medieval world offered little opportunity in comparison with that

offered by modern experimental science. As mechanics was in the

early seventeenth century the ideal field for the exercise of the

1 Charles Singer: Studies and Essays in the History of Science and Learning offeredto George Sarton (New York, 1947), p. 47.


conceptual intellect of Galileo, so anatomy in the sixteenth was a

fruitful subject for keenness of observation and, to a less degree,

ingenuity of experiment. Unconsciously the new developments in

the study of anatomy ran counter to the humanistic endeavour.

At the very moment when humanists were rediscovering the

philosopher in Galen his scientific authority was being under-

mined. As with so much original effort in the first stages of the

scientific revolution, a more perfect anatomical knowledge con-

tributed not to the integration of science but to its disintegration,in this case to the elaboration of a specialized art of detached

description through which alone accuracy could be attained. Theanatomists who freed themselves, however partially, from their

natural inclination to follow classical masters were framing a newstandard of scientific observation. In no real sense was this the

moment of the birth of some novel, self-conscious method of

observation and experiment in science, but it was the momentwhen the accepted narrative of fact and theory was first modified

effectively and permanently by recourse to nature. A body of

original facts relating to a single discipline was for the first time

gathered together for comparison with the traditional account.

Justified only by practical experience, even opposed to the theories

of those who described them, the new discoveries combined to

teach the lesson that the whole doctrine of anatomy must be re-

formed by the use of meticulous observation and independent

thinking. While the facts of experience to which appeal had been

made in the framing of medieval physical theories had mostlybeen commonplace, or accidentally revealed, the new anatomyturned to the systematic exploitation of a specialized and laborious

technique.The most complete, and the most striking, use of this technique

was certainly in the De Fabrica of Vesalius. All authorities on the

subject agree that Vesalius' exposition of human anatomy is out-

standing in early modern times, basing theirjudgement on his text

as well as on his still more eloquent illustrations. But he was not

unique in his originality; rather he was the most successful ex-

ponent of a new procedure that was beginning to gain adherents

over all Europe, some of whom Vesalius did not scruple to treat

unfairly. Among his immediate predecessors Berengario, whose

illustrated Commentary on the anatomy of Mondino was publishedas early as 1521, was notable for hesitancy in following Galen.


Another, Charles Estienne, was at work on his book On Dissection

by 1532, though this remained unprinted till 1545.* Estienne was

the first anatomist (after Leonardo) to prepare figures illustrating

complete systems (venous, arterial, nervous) and he discovered

the structures in the veins, later known to be valves, which stimu-

lated William Harvey to the discovery of the circulation of the

blood. John Dryander published two illustrated treatises in 1537and 1541. Canano's incomplete myology also appeared in the

latter year (or 1540), and nine years after the publication of De

Fabrica, a set of copper-plates to illustrate human anatomy was

finished by Bartolomeo Eustachio (1520-74), which have been

described as more accurate than Vesalius5

figures, and almost

equally crowded with new observations. 2 Some of the unillus-

trated treatises on anatomy, such as those of Sylvius and Massa,are not less remarkable for skill in dissection and acuity in criti-

cism. Moreover, in the application of anatomical knowledge to

physiological theories a subject in which Vesalius was steadily

conservative another contemporary, Jean Fernel (1497-1558),was far in advance of his time; and, soon after 1543, Serveto,

Colombo and Fallopio were putting forward notions on the dis-

tribution of the blood about the body of which no hint is to be

found in De Fabrica.

When Vesalius is matched against his not unworthy rivals, his

peculiar fame appears all the more enigmatic. He did not lead

the way in making discoveries alien to Galenic anatomy, nor did

he ever intend an onslaught upon it. He had no greater learning,or more vivid freshness of mind, than his more experienced con-

temporaries. Even when spoken of by his teacher Giinther as*

a

young man, by Hercules, of great promise . . . very skilled in dis-

secting bodies,5

the observation for which he was thus praised had

already been anticipated in Italy. The task which he set himself

would seem to require ample time and mature knowledge, but

Vesalius had neither. During the mere three or four years givento De Fabrica he was busy with other writing, teaching and travel.

His whole study of female anatomy was based on the hasty dis-

1 De dissectione partium corporis humani, a large octavo, has fifty-eight full-pagewood-cuts, in which unfortunately the important portions are often too small

to be clear.2 Charles Singer: Evolution ofAnatomy , p. 135. Eustachio's figures, after being

first printed in the early eighteenth century, were thereafter frequently

republished as having contemporary value.


section of three bodies not surprisingly, it forms one of the weakest

portions of his work. Comparison of the Tabula Sex with De Fabrica

compresses his development as a scientist into an almost incrediblybrief space of time, if it was entirely unaided. Little is known of

his personality; in comparison the biography of Copernicus is

full. Often abusive, truculent, Vesalius was not a learned man bythe standards of his age, and he reveals little in the way of philo-

sophic depth such as was then expected of a scientist. He was am-

bitious, and apparently ambition prompted his one great work;after leaving Padua in 1543 to become an Imperial physician his

career in science ended.

It is impossible to fit Vesalius into the conventional picture of

the scientific worthy. But whatever may be the truth concerningthe collaboration of artist and anatomist in the production of De

Fabrica, however serious the charges that may be brought againstVesalius' character as an author, the book itself stands as a monu-mental achievement of sixteenth-century science, and in its owntime it was almost immediately recognized as such. De Fabrica was

the implementation, in a manner whose total effect is superior to

that of any contemporary work, of a single conception of what an

anatomical treatise ought to be, and there is no evidence that this

conception was not Vesalius' own. It aimed at a systematic, illus-

trated survey of the body part by part, layer by layer. The skeleton

and the articulation ofjoints, the muscles, the vascular system, the

nervous system, the abdominal organs, the heart and lungs, the

brain, were described and depicted with a detailed accuracy never

previously attained. The wood-cuts are indeed on occasion better

than the text they illustrate, though in one place it is admitted that

a drawing had been modified to fit Galen's words. In his section

on the heart Vesalius mentions probing the pits in the septumwithout finding a passage; broadly, however, he accepted the

Galenic account of the heart's function. Some whole topics (the

female organs, the eye) were less well discussed owing to errors in

observation, due in part to Vesalius' inability to free himself com-

pletely from traditional ideas. In minutiae there was much for the

anatomists of the later sixteenth century to amend.As a reformer despite himself, Vesalius' attitude to orthodox

instruction was cautious. Where his departures from Galen's texts

are most notable, generally he said little more than others at the

same time were saying.


If it be said that he often corrected Galen it may be rejoined that

much more often he follows Galen's errors. . . . The Fabrica is, in

effect, Galen with certain highly significant Renaissance additions.

The most obvious and the most important is the superb applicationof the graphic method. 1

But the graphic method was not invented by Vesalius, and to what

extent its quality was due to the draughtsman employed (who,

according to the art-historian Vasari, wasJohn Stephen of Calcar)2

will probably never be known. Although Vesalius hotly criticized

Galen for describing human anatomy by analogies drawn from

animal dissection, he was himself led into mistakes resulting from

this very practice. In his interpretation of the functions of the

structures described he followed Galen closely. His boastful narra-

tive of his own achievements, and his claims to originality are not

to be trusted without scrutiny; thus it is obviously untrue that

human dissection was utterly unknown in Italy before he intro-

duced it at Padua. Vesalius seems to have resented, rather than

welcomed, originality in other anatomists. It is true that both his

successors at Padua, Realdo Colombo (who had worked with

Vesalius) and Fallopio, made important additions to knowledge,but Vesalius himself launched an attack upon the latter's innova-

tions. The tradition of anatomical study was not inaugurated in

northern Italy by Vesalius during his short residence there, for

it had existed for centuries. As for the claim that Vesalius was the

first teacher of anatomy in modern times to carry out dissections

before the students with his own hands the idealized scene is

represented in the frontispiece to De Fabrica the view has recentlybeen put forward that even as early as 1528, and in the humanistic

medical school of Paris,'

the participation of students and doctors

in the actual process of dissection was recognized.'3 It seems,

therefore, that if Vesalius introduced any new teaching method to

Padua it was but the method he had known at Paris,

In him there was neither the burning passion of a Galileo to

refine truth from error, nor the remote vision of a Kepler: yet the

work of a man whose spirit is calm, almost plodding, may mark a

1 Charles Singer: Studies and Essays in the History of Science and Learning offered

to George Sarton (New York, 1947), p. 81.2 This attribution has been disputed and defended; cf. W. M. Ivins in Three

Vesalian Essays (New York, 1952).8 Charles Singer: Bulletin of the History of Medicine^ vol. XVII (Baltimore,

1945), PP- 435-8-


turning-point in exact science. If Vesalius was pre-eminent amongearly anatomists he must not be made so at the expense of his

contemporaries, who were also men of ability and precision, nor

by neglecting his own faults and mistakes. Although the structure

of De Fabrica was excellent, Vesalius was a poor expositor;

nevertheless, his text inculcated the principles of the new mode of

anatomical study more effectively than any other work, and

brought back the study of anatomy to the dissecting-table. He was

responsible for making many useful innovations in the techniqueof dissection which extended its possibilities. He had the merit of

seeing anatomy as more than a catalogue ofstructures useful to the

physician seeking the proper vein from which to let blood or to

the surgeon tracing the course of a bullet-wound; it was for himan entrance into knowledge of the living body as a functional

organism. True, he was unable himself to progress far towards

this desideratum, and therefore he was content to rely uponGalen, but his work was a guide to his successors. De Fabrica must

be judged as a whole, and it is in the preponderance of its virtues

over its defects that the book excels. In a descriptive subject such

as anatomy, especially where the relations between the possibilities

of research and the necessities of teaching are very close, there

seems to exist a critical level of accuracy. Until description has

passed the critical point no steady accumulation of knowledge is

possible because there is no firm orientation to study, no sound

model exists, doubt and duplication lead to wasted effort and

repeated surveys of the same elementary facts. Once the critical

point is passed and the outline is securely drawn, so that the

student can easily identify it with the natural subject, it is possible

to press forward to deeper and finer levels of detail. Vesalius'

contemporaries had almost attained this point; in particularstudies some passed far beyond it; but De Fabrica passed it in an

extended account of the whole body. The work was far from

impeccable, perhaps its originality and the importance of a highaesthetic (which is not the same as a naturalistic) quality in its

illustration have been over-emphasized, but it was sufficient. 1

The map was made. It is not enough to say that Vesalius

1 There are some hundreds of figures, not including the initials, in the first

edition of the De Fabrica. Of these, only about a score enter the "aesthetic"

class: they are, of course, the finest wood-cuts in the book, but they do not

compose the whole of Vesalius' graphic teaching.


redirected anatomists to the natural facts of bodily structure, for

the work of contemporary anatomists was already in the same

direction, and in any case it was to be long before the meaning of

these facts (like the valves in the veins) could be correctly inter-

preted. The main point is that the ^De Fabrica was the actual

source from which the method of obtaining the facts of human

anatomy by dissection and experiment was learnt; admittedlyit could still have been learnt had the" De Fabrica never been

printed. In the hands of students it was an instrument fit to

measure against nature, to serve as a guide to the complexitieswhich Vesalius' successors discovered in their turn, and to create

in the exceptional man the critical frame of mind which is the

main-spring of research.

In a sense the possession of this quality belongs to the definition

of modern science. In many instances the reason for the sterility

of conventional science before 1500 was not simply that its

exponents were engaged upon a vain endeavour, nor most

obviously that they were fondly prejudiced, perverse, or unoriginalof mind. They, like all men, could do no more than accept or

modify according to their powers an intellectual inheritance

which was a part of the age and society in which they lived. Suchan inheritance is never exactly consistent, nor is it wholly dominantover the individual, but the range of possible variation from it is

always limited. One characteristic of the intellectual heritage of

every medieval philosopher, or physician, was the limited area of

contact between the system of ideas in science and the reality

of nature; on the one hand was a natural philosophy satisfactory

enough to those who knew no other, and on the other the bewilder-

ing complexity of the natural world. A juxtaposition of the two

was not easily effected. If it seemed that philosophy explained the

world, it seemed so because the distinction between the philosophicview of natural phenomena, and the phenomena themselves, was

not clearly revealed; and since the globus intellectualis and the

globus mundi were so far distant, constructive, purposeful criticism

of the former could hardly emerge from its comparison with the

latter. Hence arises the importance of a new field of experience,such as magnetism offered to the middle ages, or of a new attitude

to scientific explanation, such as that contained in the mechanistic

philosophy of nature. The effect of every major idea in science, of

every major observation and experiment, has been to present a


new juxtaposition of the realm of thought and the realm of facts,

which may in turn demand a far more profound readjustmentthan the original innovator could foresee.

It is easier to illustrate this from the history of ideas than from

the history of factual discoveries, easier to see it in Copernicus,for example, than in Vesalius. It is obvious now that once the

central tenet of the old astronomy was rejected, the incidentals

which Copernicus had retained must also be challenged. Yet it is

important, for the understanding of the process and developmentof the scientific revolution, to see how the cardinal observations

and measurements emerged, as well as the cardinal concepts. Thenormal development of any established department of science maybe, and indeed usually is, conditioned in large part by its con-

ceptual structure and the nature of the theoretical techniques

appropriate to it, since these furnish the perspective in which the

problems are to be seen. In exceptional situations, however, the

disclosure of a new fact commonly the apprehension of the im-

port of a whole group of facts may force a crisis. Then existing

theory may prove an obstruction. A. novel perspective is called

for. In this respect stands the work of Vesalius to that of Harveyand later physiologists, who revolutionized ideas by applying

experimental procedures to the elucidation of the bare facts

yielded by a more exact anatomy. Through the effort of Vesalius

and his less famous contemporaries there was introduced into

biological science for the first time an acute sense of the importanceof minutiir, of the mastery of special methods, and of the precise

and full reporting of observations. Contemporaries admired the

De Fabrica as the perfection of descriptive art, to this also its claim

to mark a turning-point in the growth of scientific knowledge is

due. But the book is not less notable as entailing the challenge to

Galenic theory which its author scarcely contemplated.De Revolutionibus Orbium Coelestium has an altogether different

character. Its force springs from the other tactic of the scientific

revolution, accepting the body of observation on which conven-

tional science relied and even the method by which the facts

could be grouped into a theoretical interpretation, but denyingthat only the conventional interpretation was possible, or even

preferable to its alternative. Although his name has become more

famous, Copernicus was in many ways less modern than Vesalius,

in particular he had a far less acute sense of the reality of nature:


like many medieval men he was far more concerned to devise a

theory which should fit an uncritically collected series of obser-

vations than to examine the quality of the observational material.

Tycho Brahe, half a century later, was the Vesalius of astronomy.If one can discern a fundamental motive for Copernicus'

reconstruction of the cosmos, that too seems to be medieval.

The unity of thought had been the goal of medieval philosophy:the harmonizing of pagan science and Christian religion, the re-

conciliation of authorities, the explaining of contradictions and

discrepancies, had been its unending task. And it seems that the

belief that true knowledge must be unified provoked Copernicus'first doubts. The early sixteenth century was not a time at which

dogmatism on astronomical problems was easy or profitable. The

popular view that the astronomical science of the middle ageswas simply a matter of applying rigid principles in a determined

fashion is mistaken. Of course the main structure of astronomical

theory was firmly established, but the working out of the exact

details involved constant experimentation, and the best authors

were not themselves agreed on the true values to be attached

to all the constants of the Ptolemaic system. In fact medieval

astronomers were well aware that that system was not meticulouslyaccurate as a calculating instrument and, though they did not

revolt against its fundamentals, they attempted by adjustmentsand additions to bring it to perfection. Wherever astronomy was

actively studied, there was a renewed interest in observation,in modifications to the machinery of the spheres, and renewed

computation of the constants and tables. The greatest problem of

all was of a different order. No man of learning could ignore the

fact that the system of Ptolemy was^^ an

elaboration^ of that of Aristotle. To describe as physical the

Aristotelean picture of the cosmos, and to describe the Ptolemaic

as a mathematical hypothesis of planetary motions, is perhaps to

press an analysis of which the middle ages were barely conscious.

Yet, while there was no direct or irresolvable antithesis, it was

always clear that there was something of a hiatus between

cosmological physics and astronomy. There was not merely a

perpetual struggle to reduce the complexities of planetary motionto mathematical order, but also these complexities were confusingin physics. The eccentricity of the earth with respect to certain

spheres, and the irregularity of the motion of these spheres about


the earth, were assumptions which practical astronomers were

forced to make, without possibility ofreconciliation with Aristotle's

physical doctrine. Oresme pointed out another difficulty that

arose from the introduction of epicycles, concluding that Aristotle

was obviously mistaken in his demonstration that the intelligences

controlling the spheres do not themselves move. 1 He seems to

distinguish, too, between what is true "in philosophy" and true

"in astrology," i.e. astronomy. In more practical ways the im-

perfections of astronomy were recognized. The calendar was out

of joint. Even astrologers admitted that their calculations were

uncertain because of the inaccuracy of the tables with which theyworked. Tables for the cycle ofmoon and tides, essential to seamen,were unreliable. The observational basis in the celestial coordin-

ates of the fixed stars, and the latitudes of places on the earth, was

equally open to doubt. Humanism added its own confusion: the

conflict between Arabists and Humanists was less spectacular in

astronomy than in medicine, but it was not the less real in the

difference of opinion between those who wished to preserve the

simpler system of Ptolemy, and those who believed that Islamic

elaborations, like the trepidation of Thabit, were necessary.

Already in the fifteenth century Peurbach and Regiomontanushad applied themselves to the technique of observation, and tried

like their predecessors to bring astronomy up to date by newdeterminations and computations. They did not appeal to nature

against Ptolemy, but they sought to refresh his system by a new

draught of observation. The world of learning upon which

Copernicus entered knew that a reform was needful, even thoughit did not welcome the shape of that reform in his hands. A world

expecting some new mathematical formula which would "save

the phenomena"along the old lines received instead an unprece-

dented synthesis of philosophy and mathematical astronomywhich attacked much that was orthodox in both. Although united

in the higher realm of ideas, the philosopher and astronomer

had long been professionally divorced. Those who contemplatedthe mysteries of the cosmos had done little actual observing or

calculating, while the practical astronomer had lost himself in

mathematical abstractions. Copernicus was a superbly equippedtheoretical astronomer (with some skill in observation, but no

great love for it) who shows at the same time a strong sense of

1 Medieval Studies, vol. IV, p. 169,


physical reality. He was affronted by the Aristotle-Ptolemydualism. He thought that some of the devices used by Ptolemy,^

equant-EointAwere cheats counter to sound

philosophy. He found that the physical system failed in mathe-

matics, the mathematTcaF in physics. The only solution to the

dilemma required two steps: the purging from mathematical

astronomy of its needless reduplications, and from physics of

those ideas which were obstacles to a true conception of the

universe. Thus the reform of astronomy demanded a limited

reform of physics, and Copernicus was in fact impelled to dis-

tinguish between those doctrines of Aristotelean physics which he

took to be true, and those which he took to be false. In the end

much was to turn upon the justice of his conception of what is

4 *

right" in nature.

There is good evidence that Copernicus was highly esteemed

by men of learning long before the publication of De Revolutionibus,

which indeed in the eyes ofsome contemporaries diminished rather

than enhanced his reputation.1 Rheticus describes him as 'not

so much the pupil as the assistant and witness of observations*

of Domenico Maria da Novara, himself something of a critic of

Ptolemy, at Bologna: and as lecturing on mathematics at Romein 1500 (when he was twenty-seven) 'before a large audience of

students and a throng of great men and experts in this branch of

knowledge.'2Clearly Copernicus had already become an accom-

plished student of mathematics and astronomy in his earlier daysat Cracow. On his second visit to Italy in 1514 he was consulted

on the question of calendar reform. One of his critical writings,

the Letter against Werner (1524), seems to have circulated in

manuscript, as did the first sketch of his new astronomy, the Little

Commentary which was written, probably, about 1530. There is a

record of Copernicus' ideas being explained to Pope Clement VIIm X 533' I*1 T 539 his fame attracted the Protestant Georg Rheticus

from Wittenberg to Frauenberg, "remotissimo angulo terrae," to

become his pupil, and in the following year Rheticus' First Account,

a review of Copernicus' manuscript of De Revolutionibus, was

published at Dantzig. Some of his readers, who like GemmaFrisius and Erasmus Reinhold later became firm advocates of

1

Lynn Thorndike: History of Magic and Experimental Science, vol. V (Balti-

more, 1941), pp. 408-13.* Edward Rosen: Three Copernican Treatises (New York, 1939), p. in.


the heliostatic system, awaited the publication of the whole workwith eager anticipation. In the preface to his book, dedicated to

Pope Paul III, Copernicus particularly mentions, as friends whoremoved his reluctance to publish, Nicholas Schoenberg, Cardinal

of Capua and Tiedeman Giese, Bishop of Culm. While his

investigations thus received a measure of countenance at Rome,it was Luther who was to speak of

*

the fool who would overturn

the whole science of astronomy.'1

Despite this, the new doctrine failed to secure adherents.

Favourable references to it are scarce throughout the sixteenth

century: most arc couched in terms resembling Luther's. 2

Admittedly the book was difficult, written only for those who were

skilled geometers and experienced in astronomical calculation,

and it supported a proposition which had been condemned in

philosophy for two thousand years, and no astronomical advan-

tages even if they were genuine could vindicate it. If the

celebrated note by the Lutheran minister Osiander which,unknown to Copernicus, declared that the tenets of the followingbook were to be taken only as a mathematical hypothesis, a

calculating device, and not as truth, had any effect in warding,off official censure (which seems doubtful), it certainly did nothingto weaken the general sentiment that speculation on the earth's

movement was foolish and futile. Those who are known to have

held the opposite view in the years 1543-60 can be numbered onthe fingers of one hand: Reinhold, who calculated the first set

of astronomical tables in accordance with Copernican theory;Robert Recorde, the English mathematician; John Field and

John Dee, English astronomers; and Gemma Frisius of Louvain^one of the most famous astronomers of the age.

3 There is nothing,other than Copernicus' own book, that can be called an expositionof the heliostatic hypothesis in the later sixteenth century. Until

after the condemnation of Giordano Bruno in 1600 Copernicus'name was suppressed not by authority, but by indifference.

|

To understand this, it is necessary to understand in whatmeasure De Revolutionibus was revolutionary, and effected a

reform in astronomical thought. In the heliostatic principle, and1 De Revolutionibus Orbium Codestium (Nuremburg, 1543), sig. iii recto.2Dorothy Stimson: The Gradual Acceptance of the Copernican Hypothesis (New

York, 1917).3 Gf. Grant McColley: "An early friend of the Copernican theory : Gemma

Frisius," Isis, vol. XXVI (1937), p. 322.


in its necessary physical consequences, Copernicus opposed the

common sense of his age: in everything else he was conservative.

There was nothing in the method of his madness to arouse

contemporary interest. Moreover his madness took the form of a

familiar heresy: therefore again the whole theory could be lightly

dismissed. A whole stream of references proves that to supposethat the sixteenth century ought to have reacted violently in

approval or condemnation of the book when it appeared is to

misunderstand a whole facet of medieval astronomy. That certain

of the ancients had supposed the earth to move was as well knownto the middle ages as Aristotle's powerful reasoning against their

contentions.1They found the question debated again by their

Arabic authorities. As a result, several scholars of the fourteenth

century exhibit a marked tolerance in their treatment of the idea

when commenting upon Aristotle, among them many members of

the"impetus" or experimentalist school, including William of

Ockham, Albert of Saxony, Jean Buridan, and Nicole Oresme.

Oresme, in his commentary on De caelo, denies that the stability

of the earth is a logical consequence of the movement of the skies:

from the analogy of a revolving wheel he shows that it is only

necessary in circular motion that an imaginary mathematical

point at the centre be at rest. Further he says that local (i.e.

relative) motion need riot necessarily be referred to some fixed

point or body: rest is the privation of motion, and is in no wayinvolved in its definition. For instance, he says, there is imaginedto be outside the universe an infinite motionless space, and it is

possible that the whole universe is moving through this space in

a straight line. To declare the contrary is an article condemnedat Paris, yet this motion could not be considered to be relative to

any other fixed body. Suppose that the skies stood still for a dayand the earth moved: then everything would be as it was before. 2

In another place he gives his judgement, "under all correction,"

Hhat it is possible to maintain and support the opinion that it is

the earth which is moved with a daily motion (axial rotation) andnot the sky, and further that it is impossible to prove the contrary

by any experiment (" experience"), or by any reasoning. This

was just what Galileo was to declare nearly three hundred yearslater. Against his proposition Oresme quotes three arguments,

1McColley:

" The theory of the diurnal rotation of the earth," ibid. p. 392.a Medieval Studies, vol. IV, pp. 203-7.


all ofwhich were to be directed against the Copernican hypothesisin the sixteenth and seventeenth centuries. Firstly, the skies are

actually observed to revolve about their polar axis; secondly, if

the earth turned through the air from west to east, a great windwould be felt constantly from the east; and thirdly a stone thrown

vertically upwards would not fall back at the place whence it was

thrown, but far to the west. Oresme has replies to all these objec-tions. In answer to the first, he emphasizes the relativity of all

appearance of motion: a man seated in a boat gazing at anotherboat cannot tell whether his own vessel is moving, or the other in

the opposite direction, but there is a prejudice in favour of the

stability of one's own immediate frame of reference. As for the

wind, the earth, water and air of the sublunary world all movetogether, and so there is no wind other than those to which we are

accustomed. To the third objection Oresme replies that the stonethrown up in the air is still carried along in the west-east direction

with the air itself, and with 'all the mass of the lower part of theworld which is moved in the daily movement. 5

It is not quiteclear what this last phrase meant to Oresme, but it holds an ideaof profound consequence. The stone falls back to the place whenceit came, as it would do if the earth were still, and Oresme pointsout (again anticipating Galileo) that all the phenomena of motion

appear to be identical in a ship which is moving or a ship whichis at rest. As Oresme puts it, in less precise language, a movementwhich is compounded of motions in two directions is not discern-

ible as such when the observer himself participates in one ofthem.

Various theoretical or physical arguments against the rotation

of the earth anticipated by Oresme turn upon the idea that it

would be unnatural and out of place in the texture of natural

philosophy. This Oresme also denies. He points out that the

Aristotelean system attributes no movement to the earth as a

whole, though Aristotle himself declared that a single simplemotion was appropriate to each element so that the earth mightwell turn in its place, as the heavens do, or as the element fire

does. Oresme agrees that if the earth turns it must possess a "mov-ing virtue,'* but this it must have already, since displaced parts ofthe earth return to it. To the criticism that the motion of a movingearth would falsify astrology, he makes a most important riposte.All conjunctions, oppositions and influences of the sky would take


place as before, and the tables of the movements of the heavenlybodies and other books would be as true as they were before, onlyit would now be recognized that the daily rotation was apparentin the heavens, and real in the earth. It has often been allegedthat Copernicus destroyed whatever scientific basis astrology

might be supposed to have had. It was not so. The practice of

astrology has been entirely unaffected by it, just as it was (and is)

unaffected by the fact that the "Houses" of the zodiac no longer

correspond with the constellations after which they were named

owing to the precession of the equinoxes. The predictions of

judicial astrology turn upon the configuration of the skies at anymoment: they are unconcerned with the mechanics of the motions

by which those configurations are produced. And Oresme's dis-

claimer was actually re-echoed in the sixteenth century. To quoteThorndike: 'It is a historic fact that the Copernican system was

first publicly announced, if not precisely under astrological aus-

pices at least to an astrological accompaniment and that such

signifying the future was for long after associated with it in men's

minds.' 1 Two of the leading exponents of the new scheme,Rheticus and Reinhold, had no doubts of the virtues of judicial

astrology, and Copernicus himself never declared against it.

The authority of Scripture was constantly brought to bear in

favour of the geostatic doctrine, but even this does not silence

Oresme. Joshua's miracle can be interpreted in the sense that the

sun apparently stood still, while the earth was really halted. He seizes

upon the point that if the earth be supposed to move from west to

east, all the celestial motions will take place in the same sense,

which he thinks increases the harmony of the system. Also it would

place the habitable part of the globe on the right or noble side of

the earth. Again, it will be found that in this way the celestial

bodies which are farthest from the centre will make their circuits

more slowly (instead of more quickly as in the geostatic theory)which seems reasonable; and the principle that God and Nature

do nothing in vain will be more faithfully observed; for example,there will be no necessity for a ninth sphere. After all this potent

reasoning has been marshalled against the conventional doctrine,it comes as an anticlimax to find Oresme returning to it. 'Never-

theless,* he concludes, 'all maintain, and I believe, that the

heavens are thus moved, and the earth not: 'Tor God fixed the orb1

Op. cit.yvol. V, p. 414.


of the earth, which shall not be moved,"1notwithstanding the

reasons to the contrary, for these are not conclusive arguments.But considering all that has been said, one might believe from this

that the earth is moved, and the sky not, and there is nothing

obviously to the contrary, which seems prima facie as much, or

more, against natural reason as are the articles of our faith.' 2

One might think that the famous cosmological debate of the

seventeenth century had been rehearsed in the fourteenth!3 There

were, indeed, subtle changes in the background in which Galileo

set the same, or similar, arguments; but if Oresme had been dili-

gently followed the stability of the earth could hardly have been

defended save as an act of faith, not by reason and observation.

The diurnal revolution was again discussed in the fifteenth century,when it was upheld by Nicholas of Cusa, and in the early sixteenth

before the appearance ofDe Revolutionibus. This diurnal revolution,

however, and the long argument in favour of it by Oresme, mustbe clearly distinguished from the theory of the annual motion of

the earth which was developed by Copernicus, not to speak of the

third motion which he attributed to it to account for the parallel-

ism of its axis in space. A heliostatic theory imposed a far moresevere strain on intellectual adaptability than a geocentric theorywhich admitted the diurnal rotation. ^Tojiayc.^conceived the

^ claim to originality* ajad. it wasthe annual ^2^nJ^îslLÎ

l(êP}Pc^ tne Copernican hypothesis

both in the ey^qfibe.majority, and also in the eyes of the Churchbecause of its heretical consequences.

It can hardly be imagined that the earlier discussion of the

diurnal motion was unknown to Copernicus, and he must have

considered its adoption as the first step to a reform of astronomya step which unfortunately did little to solve the problem of

planetary motions and the multiplicity ofspheres. It is not unlikelythat his conception of the earth as of the same kind as the heavenly

bodies, and therefore equally suited "by nature" to planetarymotion (being spherical for instance), is an extrapolation from the

reasoning used (by Oresme among others) to support the idea

that the earth is "by nature" suited to axial rotation. Certainly1 Psalm XCIII, i : 'The world also is stablished, that it cannot be moved.*2 Medieval Studies, vol. V, pp. 271-9.3 As was long ago pointed out, with too great emphasis and some misunder-

standing, by Duhcm in Revue Generate des Sciences Pures et Applique'es, vol. XX(1909).

6o THE SCIENTIFIC REVOLUTION

Copernicus had to abandon the idea of"one element, one motion,"but this had been virtually abandoned by Oresme. Not, however,until Copernicus had begun to consider this second, annual

motion could he have begun to see the possibility of results im-

portant to mathematical astronomy in this the middle ages haddone little or nothing to help him. Even Oresme's very correct

remarks on the illusions of relative motion only refer to a geo-centric system, though they were equally valid as Copernicus

applied them to the heliocentric. Unfortunately, the steps bywhich Copernicus proceeded from the first to the second motion,

if that was his course, are totally unrecorded. He relates simply, in

the Preface to his book,

Nothing urged me to think out some other way of calculating the

motions of the spheres of the world but the fact that, as I knew,mathematicians did not agree among themselves in these researches.

For in the first place they are so far uncertain of the motion of the

Sun and Moon that they cannot observe and demonstrate the

constant magnitude of the tropical year.

Then he goes on to say that there was no consistency of principlein the devices that had been used some had employed the simplehomocentric spheres, others eccentric spheres, and yet others epi-

cyclic systems. They had passed over the symmetry of the universe,

as though one should put together a body from different membersAn no way corresponding to one another, so that the result wouldbe rather a monster than a man. This uncertainty, he thought,must prove that some mistake had been made, otherwise every-

thing would have been verified beyond doubt.

Then when I pondered over this uncertainty of traditional mathe-matics in the ordering of the motions of the spheres of the orb, I was

disappointed to find that no more reliable explanation of the mechan-ism of the universe, founded on our account by the best and most

regular Artificer of all, was established by the philosophers who haveso exquisitely investigated other minute details concerning the orb.

For this reason I took up the task of re-reading the books of all the

philosophers which I could procure, exploring whether any one had

supposed the motion of the spheres of the world to be different fromthose adopted by the academic mathematicians.

Coming across Greek theories which attributed both an axial

and a progressive rotation to th^earlh* and following the example


of his predecessors who had not scrupled to imagine the circles

they required to "save the phenomena," he thought he mighthimself be allowed to try whether, by allowing the earth to move,more conclusive demonstrations of the rotation of the spheres

might be found. And he discovered that if, as he puts it, the

motions of the planets were calculated according to their ownrevolutions, with allowance for the circulatory motion of the

earth, then the phenomena of each worked out duly. Even more

important, the orders and sizes of all the celestial bodies, spheresand even the heaven itself, were so harmonized that nothing could

be transposed in any detail without causing confusion throughoutthe universe (Fig. 4).

1

Copernicus was a theoretical astronomer of genius and origin-

ality. He must have noted the suspicious reversal of the constants

of epicycle and deferent between the upper and lower planets: he

must have perceived the unaccountable intervention of the sun's

period of revolution in the calculations for each of the five planets.

Believing that the assumption of an annual motion in the earth

was no more wild than the assumption of a diurnal revolution, he

was capable of taking the celestial machinery to^fccesand re-

assembling it in accordance with a different patWn. Workingfrom irrefutable observations, he proved that the new pattern

gave as good results as the old.

It could hardly give much better results because the parts of the

machine of the world as revised by Copernicus were essentially

gf the same dimensions as before, though arranged in a different

order. His determining observations were those of the Greek

astronomers, Timocharis, Hipparchus, Ptolemy, supplemented bythe work of their Moslem successors Arzachel, al-Battani and

Thabit, and his own measurements, few in number arid mostlymade about 1515. Sometimes, as in his determination ofthe lengthof the sidereal year, his result was less accurate than an earlier

one (that of Thabit). Copernicus admitted most of the variations

or anomalies which had been introduced to account for the ap-

parent changes in some constants (for example, the variation in the

obliquity of the ecliptic causing an oscillation which v/as correctly

explained by Copernicus for the first time; and various com-

plexities in the motion of the sun, which he transferred, of course,

1 De Revolutionibus, Preface. The English version in Stimson, op. cit., does not

always make Copernicus' thought fully intelligible.

MOON

Mercury llbrotes on the

diom.(380)oftheep<cyc/ewith a period of 183 d.

FIG. 4. The Copernican System of the Universe, (a) General arrangement,(b) Lunar theory, (c) The inferior planets, (d) The Earth. The dimensionsare to scale unless otherwise indicated. (</=days, e= eccentricity,

r=radius.)


to the earth). In addition he introduced new elaborations; some,like the motion of the apse-line of the earth's orbit already sus-

pected by al-Battani, were real and necessary, others, like the

"third motion" of the earth were superfluous or due to the colla-

tion of inaccurate observations, such as the variation which he

supposed to occur in the eccentricity of the earth's circle about the

sun. In fact, mathematically speaking, Copernicus did not create

a new astronomy in the sense of isolating and measuring everycelestial motion afresh; what he did do was to reinterpret the

Ptolemaic structure from the heliocentric point of view, addingsuch refinements as he believed to be necessary. His remark to

Rheticus,"If only I can be correct to ten minutes of arc, I shall

be no less elated than Pythagoras is said to have been when he

discovered the law of the right-angled triangle," shows that his

ambition in the matter of precision was very limited. And it provedin fact that when the first astronomical tables were calculated in

accordance with the new hypothesis, they were little if at all

superior to those which had preceded them. 1

Astronomy remained the doctrine of the sphere, and the imagerydrawn from it which is so prominent in sixteenth-century imagi-native writing was hardly less appropriate to the new theory than

to the old. Having rejected the prime assumption of cosmology,

Copernicus had no occasion to challenge others. His geometry of

the heavens is still that of rolling orbs, save that the earth has re-

placed the sun in the third sphere. He preserved the fundamental

division between the sublunary region and the celestial, between

the natural laws of earth and sky. He insisted even more severely

than Ptolemy upon the inviolable perfection of circular motion,

repeated again the proof that the alternative methods of eccentric

sphere and deferent-with-epicycle are identical in their results,

and reduced all motions to combinations of these two forms. The

reality of the crystalline spheres was unquestioned. Apart from

his one great innovation, all Copernicus' astronomical thoughtis thoroughly medieval. Truly he reformed the medieval universe,

because he brought its pattern into a new order, but he introduced

no new doctrine concerning its composition or the deeper logic of

its various appearances.

What, therefore, were the merits of the new astronomical

system? What arguments could be adduced to show that in this

1 Cf. Appendix B.


complicated dance of relative movements the stability of the sun

was more real than the stability of the earth? Copernicus dealt

with these two questions as one, but as will be seen they require

separate answers. In the first place, the pattern of celestial motion

described by Copernicus and the methods used to work it out in

detail had several distinct advantages. On the whole, the devices

were rather more^economically displayed, though this is a feature

whose importance has been exaggerated and, since the observer's

point of view is geocentric in any case, the geocentric conceptionhad some advantages in tne ease of handling. The fixed stars were

fixed indeed, and with the whole system no more than a point in

comparison with the size of their sphere as Copernicus realized

from the fact that they revealed no annual parallax the problemof predictive astronomy was properly limited to the planetary

bodies(. /These now recovered their independence without the

intervention of any extraneous factor in their revolutions, and the

main pattern of th&rplanetary mechanisms could now be madeuniform for all five; "Moreover, Copernicus was able to declare,

for the first time, the relative sizes of the planetary spheres, thoughbecause he followed Ptolemy's estimate of the earth's distance

from the sun the whole system was far too small. 1 As the lower

planets, Venus and Mercury, were now placed between the earth

and the centre of the universe the peculiarities of their motions

and their special relation to the sun were explainedNblearly theycould never be observed at a greater distance from it than the

lengths of the radii of their spherei^The "stations" and retro-

grade motion of the planets, which had favoured the epicycle

theory, could now be seen as pure illusions caused by the addition

and subtraction of the earth's movement and the planets' relative

to the unchanging background of the starry sphereL/The equantsand uneven revolutions of the Ptolemaic system were removed andthe principle of perfect circular motion observed more purely.

Again, the fluctuations in the apparent size of the heavenly bodies

(as the earth approaches or recedes from them) required by the

Copernican geometry corresponded more closely to observation

than those required by the Ptolemaic, particularly in the orbit of

the moon, which Ptolemy supposed to vary by a factor of nearlytwo. MQsL-Qf the advantages that can be ^obtained by supposing

1 About 5 per cent, of the true value: the dimensions are derived from the

Ptolemaic planetary constants (see above, p. 1 6) .


the sun to lie near the centre of all the orbits were actually workedout by Copernicus in his calculations, which thus removed some

redundancies^ and threw light on many obscure points.

On the other hand, it could not logically be claimed that these

advantages proved the sun to be at rest and the earth moving. \

An interesting variant of the conventional geocentric theory,described by Martianus Capella in the fifth century A.D. made the

lower planets revolve about the sun, and there are references to

the same idea to prove it was not forgotten in the middle ages.1

A natural step beyond this was to suppose all the planets to revolve

around the sun, while the sun turns about the fixed earth, and it

was taken by the great Danish practical astronomer Tycho Brahe

towards the end of the sixteenth century. Mathematically and

observationally the Tychonic system and the Copernican are

indistinguishable, in fact the Tychonic is an exact representation

(in Copernican terms) of what the observer actually sees with

his instruments. Whatever advantages the Copernican pattern of

motion had over the Ptolemaic could equally well be claimed for

Tycho's defence of geocentricity. History has not been kind to

Tycho's hypothesis, and it has seen (with Galileo) the great

cosmological debate as being conducted between Ptolemy and

Copernicus. It is a misleading view. Tycho had enormous

authority, and his system was quoted as the third possible hypo-thesis until late in the seventeenth century. It reconciled the

combatants without compromising any essential issue; it took all

that was scientifically sound from Copernicus, and for the rest

clung to common sense. If we would understand the power of the

geocentric notion over men's minds we must give it its best

defence, not its worst, and this Galileo naturally did not do. Todismiss Tycho Brahe's contribution as a rather pointless and

unnecessary obstacle to the advance of truth, or as a conservative

aberration on the part of the creator of modern positional

astronomy, is to misrepresent entirely the scientific situation andthe scientific mind of the sixteenth century. Its importance is

that Tycho pointed out, with absolute justice, that there was no

particle of evidence to be derived from astronomy which could

decide whether the earth moved or not, whereas there was much

good evidence of another kind to lead one to conclude that the

1 Heraclides of Pontus taught this system, with the addition of the diurnal

rotation of the earth; it is mentioned approvingly by Copernicus.


earth does not move. Therefore, while the ingenuity of the

Copernican geometry of the heavens is to be admired, and was in

fact admired by many who opposed his chief premiss, it must be

recognized that for the sixteenth century this was irrelevant to

the main issue, which turned upon different considerations

concerning the earth's mobility.Taken by themselves, and omitting the mathematical improve-

ments on Ptolemy which are quite neutral in their effect,

Copernicus* arguments in favour of the moving earth were

scarcely compelling in their contemporary scientific setting. Norwere they very novel. He answered the traditional objections muchas Oresme did, developing the thesis that the globe is naturallyfitted for circular motion. The earth is absolutely round; it is the

property of a sphere to revolve in a circle, expressing its form in

its motion; ergo the earth revolves. By this reasoning the movementof the earth is natural, not violent: why then should it fly to

pieces, as Ptolemy supposed? It would rather be much more likelythat the almost infinitely distant sphere of the fixed stars should

disrupt under its own velocity, if it were forced to turn round oncein twenty-four hours, than that the earth should do so. Air andwater move with the earth, so terrestrial phenomena are unaffected.

The absence of measurable stellar parallax is explained by the

immense distance of the stars, and it is argued that it is easier to

believe that the earth moves, than that the whole heaven movesabout it. If, as Aristotle seemed to maintain, the condition of rest

and permanence is more noble and divine than that of changeand instability, Copernicus replies that rest should in that case beattributed to the whole cosmos, and riot to the earth alone. In

discussing the effect of terrestrial motion upon the doctrine of

gravity and levity, he enunciates an idea of surpassing fertility:

Gravity is nothing but a certain natural appetite conferred upon the

parts by the divine providence of the maker of all things, so that theyshould come together in a unity and as a whole in adopting a spheri-cal form. It is credible that this property exists even in the Sun,Moon, and other planets, ensuring the unchanging sphericity whichwe see, and nonetheless they perform their revolutions in manyways.

Once more Copernicus has emphasized the fact that the earth is

of the same kind as the heavenly bodies; and if it is, as he thinks,a planet itself, then it must have a progressive circulatory motion


as well as axial rotation. Finally Copernicus has this glowing

passage upon the sun:

In the very centre of all the Sun resides. For who would place this

lamp in another or better place within this most beautiful temple,than where it can illuminate the whole at once? Even so, not inaptly,some have called it the light, mind, or the ruler of the universe. Thus

indeed, as though seated on a throne, the Sun governs the circum-

gyrating family of planets.

It is an obvious principle of logic that the unknown cannot be

demonstrated from the unknown. Measured by this standard,

Copernicus' arguments in favour of heliocentricity are illogical.

His aim was to prove that the movement of the earth did not

conflict with the principles of physics, which of course meantAristotelean physics. But in so doing he interprets these principlesin a sense different from that of Aristotle, and that understood bymost of his own contemporaries. He is forced to allege that

gravity, a tendency to cohere, is a universal attribute of sphericalbodies. He questions whether rest is inevitable to the elemental

earth, and motion to the weightless heaven. Contemporaries can

hardly be blamed if it seemed to them that physics had been

distorted to fit a newly imagined astronomical theory. Copernicuswas not a natural philosopher but an applied mathematician, andin historical perspective it would have been no weakness in himif he had failed to subscribe to contemporary physical notions.

In the discussion of cosmological systems two possibilities were

open: either a heliostatic system could be adopted, in which case

Aristotelean physics was palpably false, and it would be necessaryto replace it by a new intellectual framework: or alternatively the

traditional physics might be held tp be true, in which case a

geostatic cosmology was enforced^To. attempt, as Copernicus did,

to reconcile traditional physics and a heliostatic cosmology was to

choose a course open to fatal criticisms.jit

was easy enough for

the opponents of the Copernican hypothesis to show that the

reconciliation could not be effected, and that its author's justifica-

tion of it in terms of contemporary doctrine was wholly spurious.The new astronomy demanded JL ew

jphjysics;and this was

ultimately to prove of great advantage to Science. But a new

physics was not Copernicus' creation, and therefore his appeal to

natural philosophy for tolerance of terrestrial motion was an appealto the unknown; his arguments could carry no conviction because


they were not derived from the physics in which men believed,

but to an unsubstantiated adaptation of it. In De Caelo et Mundo

Aristotle had welded a unity of explanation and, so long as its

fundamental concepts of motion remained unchanged, this unitywas not to be broken.

Ultimately the decision in controversies upon cosmologicalmatters which early astronomy was incompetent to decide unaided

turned upon physical considerations, and here Copernicus, with

his thoughts still modelled on Aristotle, barely hinted at a new

approach. Two things make it difficult to view his work dispassion-

ately. In the sheer majesty of its mathematical achievement DeRevolutionibus is traditional, but it is a grandly conceived and

meticulously executed demonstration of the comprehensive powersof a new hypothesis. To recalculate every motion and every

anomaly from the crude observations in accordance with an en-

tirely original pattern was a task never previously attempted.

Secondly, it is impossible to escape the compelling power of

Copernicus' intuition. Like many other original thinkers, he

uttered the truth for the wrong reasons. His work did not form the

basis of modern positional astronomy, and within a hundred yearsthe doctrine of the spheres no longer played a part in serious

science; and yet his major premiss was essential to the develop-ment of both terrestrial and celestial mechanics. His generalshipwas medieval, but the fruition of his victory lay in the future.

Lesser men might debate the logic of solar and terrestrial motions

while an imaginative mind could fasten upon the harmony, the

irresistible neatness and dexterity of the Copernican pattern.Galileo relates that he first relented towards Copernicus when he

found that the Copernicans were usually well informed in their

science, in contrast to their opponents who knew only stock argu-ments. He read the book and was converted. Men of power and

vision could learn that the new system, though incapable of

rigorous proof in detail, contained a transforming conception.The constitution of the fertile line of advance at any particularmoment is not always clear in scientific investigation; Galileo and

Kepler found it in the Copernican hypothesis. In their work

Copernicus' intuition that the earth is a planet it can hardly becalled a reasoned judgement was justified.

Even a brief survey of the total scientific activity of the sixteenth

century would require a volume to itself. Here it must be charac-


terized in a few sentences. The scientific renaissance caused nosudden break in the course ofacademic studies, nor did it suddenlyenable a "scientific method" of investigation to prove its value.

Most of the problems that were discussed belong clearly in a

medieval context, and with a few exceptions the procedure and

style of argument conformed to familiar patterns. Experimentalscience was not born in the sixteenth century. On the other hand,the study of pure mathematics flourished exceedingly, and the use

of mathematical methods in science was successfully extended. 1

Arithmetics were published in the vernacular languages and print-

ing also helped to spread and standardize mathematical symbols.The Greek geometers were edited and their work thoroughlyassimilated. Great advances were made in the formulation andsolution of algebraic equations, and in trigonometry, which in its

modern form was wholly unknown to the middle ages. The calcu-

lations involved in astronomy and in practical arts such as naviga-

tion, cartography, mining, surveying, and "shooting with great

ordnance/' became easily practicable, and books instructing in

these various forms of applied geometry appeared in considerable

numbers. When these arts were mathematized, the practitionerwho had given up rule-of-thumb methods required instruments

for the measurement of angles and distances, and the rise of an

instrument-making craft of importance can be traced somewhatearlier than the middle of the century. In many places it was

closely allied with the domestic clock- and watch-manufacture

which began at about the same time.

Opinions concerning the pseudo-sciences, astrology and al-

chemy, show no remarkable change during the sixteenth century.As in earlier times, there were disputes over the merits and sanction

of judicial astrology, but as the general sentiment was strongly

favourable there was no sign yet that the dependance of astro-

nomy on its mother-science was almost concluded. There were

no sixteenth-century alchemists whose authority stood so high as

that of the medieval Latin writer Geber, or the early seventeenth-

century adept who called himself Basil Valentine,2 but the mystical

1 D. E. Smith: History of Mathematics (Boston, 1923), vol. I, pp. 292-350.2 The former of these was traditionally an Arabic author, but it now seems

that the works ascribed to him were not composed by the real Jabir (an eighth-

century physician), though they were put together in Latin from Arabist

sources, probably in the late thirteenth century. To the latter also a false

antiquity was traditionally credited.


attitude to chemical operations was powerfully reinforced by the

personality of Paracelsus, though he was not an alchemist in the

conventional sense. Under his influence, strengthened by em-

pirical discoveries such as that of the specific action of mercury

against the "new" disease syphilis (first reported c. 1492-1500),

inorganic chemical remedies were gradually introduced into

medical practice, against strong opposition from the Galenists. 1

The use of chemical compounds in medicine stimulated a morerational interest in their preparation and properties than that of

the alchemists, but even more important, perhaps, in promotinga purely empirical attitude to material transformations amongeducated men was a new kind ofbook describing industrial opera-tions in a practical manner. Works on smelting and assaying were

circulating early in the century; the early masterpieces of tech-

nological description, Biringuccio's Pirotechnia and Agricola's Dere Metallic^ appeared in 1540 and 1556 respectively. Mining and

mineralogy, smelting and casting, the extraction of saltpetre and

the manufacture of gunpowder, the making of glass and mineral

acids, the purification of mercury and the precious metals, were

here treated in detail, systematically, and from a thorough know-

ledge of actual practice. Somewhat later similar works on machin-

ery for lifting, pumping, sawing, textile manufacture etc., in a

slightly less realistic vein, likewise did much to place engineeringon a sound basis of description.

In medicine, it is probable that the education of physicians and

surgeons improved considerably, owing to the new accessibility

of the Greek authorities, and to the new anatomical tradition

founded by Vesalius and his contemporaries. There were manyserious problems: war, which has always stimulated the progressof surgery, presented the new horror of gunshot wounds, and the

rapid growth of towns favoured the spread of disease. Public

health was less a matter of public concern in the sixteenth-century

city and state than it had been in the medieval. While, broadly

speaking, there was no great revolution in the theory and practiceof medicine, there were many advances in detail, Jesuit's bark

introduced from Peru contained quinine as a specific against the

recurring fever ofmalaria. The pharmacopoeia was standardized

1 The origin of syphilis has been exhaustively investigated. Recent opinionseems to be against the view that it was introduced into Europe from the

Americas.


first in Italy and Germany, not in England until the London

Pharmacopoeia was issued in 1618. Most dramatic of all perhapswas the influence of the French surgeon, Ambroise Pare, who led

the way in abandoning the use of the fiery cautery, previously

applied to all gunshot wounds (which were believed to be en-

venomed) as well as in cases of amputation. Although Pare still

modelled his practice broadly on that of the Chirurgia of his great

fourteenth-century countryman, Guy de Chauliac, (which was

itself often reprinted in the sixteenth century) his writings did

much to raise the prestige and skill of the surgeon. Guy, whohimself leaned heavily upon Galen and Avicenna, had taughtthat the

'

surgeon who is ignorant of anatomy carves the human

body as a blind man carves wood,' and Pare reinforced this

truth by making free use of Vesalius' De Fabrica.

The sixteenth century also saw the current of realism at workin natural y^pry Of this something more must 6e~said later

(Chapter X). The best work was still compilatory, and encyclo-

paedic on the vastest scale. It was devoted entirely to the superficial

characteristics and habits of plants and animals, and botanyremained an adjunct of medicine rather than a discipline in its

own right, but much rubbish was purged from the medieval garnerof fact and legend. The humanistic naturalists used a scissors-and-

paste technique upon the authentic texts of Aristotle or Pliny,and if the range of their reading and collation was wide and

discursive, some of them show for the first time a real eye for

genuine observation, and painstaking endeavour to confirm at

least the external features of their subjects. The first monographsin natural history have an authentic realism and attention to

specific detail which are entirely new.

On the whole, however, the scientific spirit of the century

developed naturally from the work and progress of the later middle

ages. A hasty reference to the output of the printing-press mayact as a guide to the nature ofcontemporary taste and estimations;

the most sought after and respected books were still those com-

posed long before the invention of printing.* Neither the library,

nor the academic training, of the medieval world were suddenlyoutmoded by a vast efflux of novel aspirations and methods. The

mythical "renaissance man" of the early sixteenth century,

though his tastes might be more hedonistic than those of his

1 See Appendix C.


forefathers, though he might be more enamoured of the powersand potentialities of this world and less regardful of the next, was

still largely limited in his science to the achievements of the

medieval renaissance: his very classicism only attached him more

deeply to the same roots of western learning. The cosmos of

Shakespeare is the cosmos of Dante, save that the former was a far

less philosophical poet: the Fables of Bartholomew, the complex

vocabulary of astrology and alchemy, and the doctrine of the four

humours still enclosed the framework of science which most menknew. It was not the experimentally minded Dr. William Gilbert,

with his glass rods, magnetic needles and other trivia, who was

most honoured at the court of Elizabeth, but Dr. John Dee, the

astrologer and magus, holding, as it seemed, the keys to far graver,

mysteries.

CHAPTER III

THE ATTACK ON TRADITION: MECHANICS

UNTIL

the end of the sixteenth century scientific innovations

were put forward with deference and almost a sense of

humility. A great deal of the best work of this period was

entirely non-polemicaJ : to this class belong the first stages of the

Vesalian tradition in anatomy, and much purely descriptive

writing on natural history, mineralogy and chemistry. The works

of Agricola or Rondelet were excellent contributions to science

as positive knowledge, but they created no ferment of new ideas.

It is true that Paracelsus is supposed to have burnt the books ofthe

masters before his inaugural lecture at Basel in 1527, and that he

declaimed against official medicine:

I will not defend my monarchy with empty talk but with arcana. AndI do not take my medicines from the apothecaries. Their shops are

but foul kitchens from which comes nothing but foul broths. . . .

Every little hair on my neck knows more than you and all yourscribes, and my shoebuckles are more learned than your Galen and

Avicenna, and my beard has more experience than all your high

colleagues.1

Paracelsus, whatever his other merits, was a picturesque ranter

and it is futile to portray him as a herald of the scientific revolu-

tion. The texture of his thought in which it is difficult to see anyprecise pattern was woven upon a mystical conception of nature

entirely alien to that of natural science. 2 Medicine was indeed

torn by faction: the Arabists and the Humanists, the Paracelsians

and the anti-Paracelsians, the cauterizers and the non-cauterizers

sharpened their wits in vituperative debate as they contended

1 Paracelsus: Selected Writings (edited with an introduction by JolandeJacobi), (London, 1951), p. 79.

2As, for instance, the perennial fallacy that the virtues of herbs are indi-

cated by their structure.* Behold the Satyrian root, is it not formed like the

male organs? Accordingly magic discovered it and revealed that it can restore

a man's virility. . . . And then we have the thistle: do not its leaves prick like

needles? Thanks to this sign, the art of magic discovered that there is no better

herb against internal pricking . . .' etc. (ibid., p. 186).

73


for supremacy within the profession, without aiding the advance-

ment of knowledge. Natural philosophy and natural history were

not similarly divided by quarrels arousing professional passion,

though inevitably personal jealousies were not lacking. More

typical of the relations between old and new were Copernicus

taking leave to speculate afresh on the revolving spheres, Vesalius

adapting his text to follow Galen. As yet, content if they could

show that new ideas were no worse than old ones, men were far

from asserting that the House of Learning was a crazy, ramblingwarren that needed to be pulled down and reconstructed. Withthe exception of Paracelsus, no scandalous defiance of authorityhad been noised abroad; and this was partly because the shape of

authority, the policy and content of conservatism, were themselves

unsettled at this nascent stage of modern science.

When the famous crisis was reached in 1615-16, it had alreadybeen foreshadowed in the tragedy of Giordano Bruno's life which

must be mentioned in its proper place. Bruno was no scientist,

and his impact, his historical importance, his ultimate influence

upon the development of non-scientific attitudes to science, were

all the more startling for that reason. It must not be imaginedthat the ways of the ordinary, common-sensible religious man andof the critical natural scientist were bound to deviate at the first

novelty, or that the sixteenth century was afflicted by the same

opposition of loyalties and criteria of truth that troubled the

nineteenth. On the contrary, every flaw in the conventional

account of nature was examined not in the hope that it would

profit one philosophy against another, but in the belief that its

examination would advance truth, and that in truth all matters

of importance were ultimately reconcilable. The view that a

man's access to truth might be measured by the nature of his

ideas on celestial mathematics was not known to the sixteenth

century. Copernicus' narrow vision had embraced no more than

the validity of a single hypothesis: it was with the wider philo-

sophical perspective of Bruno, and the wider scientific range of

Galileo, that iconoclasm assumed a massive, threatening character.

Disputes among mathematicians, astrologers or physicians could

be tolerated (these things were not suddenly born at the time of

the renaissance) but criticisms shaking the roots of philosophyhad to be repelled. It was not simply a question of the liaison

between Aristotle and religious doctrine, nor was Catholicism the

THE ATTACK ON TRADITION: MECHANICS 75

only opponent of innovation.1 The new scientific philosophy of

the early seventeenth century, speaking with a confident voice

that demanded credence, met sheer mental inertia and the weightof academic omniscience. Men resent admitting that they have

given their lives blindly to the defence of absurdities, and it was a

new generation, not similarly committed, that devoted itself to

the prosecution of Galilean science.

Galileo's greatest fame is as an astronomer, yet in intellectual

quaiitylfrid weight his one treatise on mechanics almost outweighsall the rest of his writings. Although his book on cosmologybecame notorious, and had a more general public influence, it

had no comparable effect upon the future development of scientific

astronomy, for its polemics were suited only to its own age. Thecontradiction here is more apparent than genuine. Thoughformally divided between two branches, Galileo's creative activity

in science was a unity, not twofold: it was a unity in laving downrevised principles of procedure in science, and again in its specific

exemplification of these principles, since Galileo saw that the

3fipnrp. of mnfinn ^nd {foe just appraisal of the results of obscrya-

tional astronomy were the twin keys to an understanding of the

universe. This is not to say that his comparatively minor (thoughin themselves major) researches, into thermometry, the properties

of pendulums, the grinding of lenses, the strength of materials,

the theory of the tides or the measurement of longitude at sea were

not conducted with the same zest for knowledge, or that they were

either irrelevant or auxiliary to his main achievement. Each one

of his minor discoveries would have been notable in a lesser man.

Each has its important place close to the origins of modern

physical science. But Galileo's physical experimentation, like his

turning of the telescope to the heavens, was original and fecund

only in the sense that it was initiatory. Other men took up his

experiments, and even drew more valuable conclusions from them

than Galileo had done, by following and expanding his methods;and while the initiation of a new kind of scientific activity is itself

an achievement of the first order, it is not of the same dignity

as the induction of fundamental principles which henceforth

1 In the first half of the seventeenth century the" new philosophy

" advancedmost rapidly in two Catholic countries, Italy and France. Criticism of its

principal tenets was no less forceful among Protestants (e.g. Francis Bacon).Cartesian science was very rapidly adopted by men of orthodox religion in

France.


dominate a whole field of science. Besides fulfilling this function

in dynamics, Galileo demonstrated the connection between its

principles, when properly understood, and the disputed points of

cosmology.Unlike his predecessors Galileo consciously assumed the attitude

of a publicist and a partisan. Writing more often in his native

language than in Latin (for Galileo was one of those who led the

way in abandoning for science the official language ofphilosophy),he shaped his arguments to a broad audience. His dialogues were

lively, his irony biting, and he did not scruple to make a merely

debating point. Zealously he magnified the weaknesses of con-

ventional science in order to turn it to ridicule. Almost alone

among the ancients the experimenter and mathematician

Archimedes was singled out for Galileo's commendation; Aristotle

he treated almost as an ignoramus, as though the subtlety and

intricacy of that intellect, preventing vision of the simple truth,

had composed fantastic webs of improbability and artificiality.

He had no doubt at all that the modern way was infinitely superiorto the ancient, and hardly mentioned any contention of the

Peripatetics that he was not prepared to deny. This habit of

opposing conventional ideas was not, apparently, a product of

Galileo's maturity nor of his great discoveries. Rather the critical

attitude which stands out even in his juvenilia was the source of

his original ideas. Born in 1564, by 1589 Galileo was already a

teaching member of the University of Pisa, where he attracted

the attention of the Grand Duke of Tuscany. Two of the most

famous stories belong to these Pisan years: here he observed the

equality in time of the swinging cathedral lamps, and carried out

(as his first biographer relates) the famous experiment ofdropping

weights from the Leaning Tower. l Unlike most academics of the

time, Galileo remained a layman. The resentment aroused amonghis colleagues by his criticisms of Aristotle prompted his removal

in 1592 to Padua, within the anti-clerical Venetian state, wherethere was a long tradition of freedom in scientific thought andwhere anti-scholastic opinions, if not exactly encouraged, were

at least tolerated. At Padua Galileo studied mechanics, constructed

1 The experiment from the Leaning Tower, told in glorification of his

master by Viviani, has been rejected by many scholars as lacking support in

contemporary documents. At any rate Galileo was not the first to subjectAristotle's dynamics to this particular test.


his first telescope, and began his long battle on behalf of the

Copernican system. After his growing fame had brought about his

recall to Florence, under the special patronage of the Grand Dukeand with an appointment at Pisa (1610), Galileo was particularlywarned to avoid utterances having a theological implication.

From 1609 to 1633 he was immersed in his astronomical observa-

tions and the polemics they provoked; then after the publicationof the Dialogues on the Two Chief Systems of the World (1632) there

followed his trial and recantation: yet having been condemned to

silence, Galileo published his greatest work at Leiden in 1638.The significance of his summons to Rome is easily exaggerated.Galileo did not compel the Roman Church to condemn Coper-nican astronomy: this intervention in scientific discussion had

already taken place decisively with the decree of 1616, and was a

natural consequence of the condemnation of Bruno. The onlyinterest in the trial concerns the nature of the judicial process,

which is not Impeccably transparent; but though Galileo maynot have broken a private pledge, he had certainly contravened

a general order. 1 Good Catholics were placed in a false positionfor two centuries by the decree and Galileo's trial under it, without

these preventing excellent work in practical astronomy in Italy,

or the uninhibited development of other new studies there. Eventhe Copernican Alfonso Borelli was able to make his suggestivecontribution to celestial mechanics (1660) by means of an

ingenious quibble.2

A reading of the Mathematical Discourses and Demonstrations

concerning Two New Sciences (1638) does not, however, give a true

picture of the revolution in dynamics as Galileo effected it, anymore than the earlier series of Dialogues can now be considered

as a balanced statement of the respective merits of the two

cosmologies. In his book Galileo the polemicist is in full cry after

the absurdities of Aristotelean physics, but in fact it is very1 However obvious this may now seem, it was not so to the ecclesiastical

censors who affixed the imprimatur to the Dialogues in 1632.2 The decree distinguished between the annual revolution of the earth,

*

utterly heretical because contrary to Holy Scripture,' and the diurnal

rotation,*

philosophically foolish.* One of its more curious results, as I learn

from Dr. Joseph Needham, was that Chinese astronomers, being instructed byJesuit missionaries, remained ignorant of the Copernican theory until the late

eighteenth century. Borelli observed its letter by overtly limiting to Jupiterand its satellites a discussion of planetary motions which he obviously intendedto apply to the earth and sun.


likely that Galileo was never an Aristotelean physicist in the true

sense, and that the original account of motion was never urged

upon him as a true and satisfactory explanation. Much patient

scholarship has been devoted to the origins and development of

Galileo's mechanics; at one stage it seemed as though its godfatherwas Leonardo da Vinci, until it was found that Leonardo was

only re-echoing a current of medieval thought. At first these

medieval discussions were regarded as no more than imperfect

gropings at a truth which Galileo apprehended perfectly. Todaythe theory of impetus appears as a theory of motion in its awnright, not an uncertain anticipation of Galileo, but a coherent

doctrine which provided Galileo with a firm starting-point. The

theory of impetus could not develop the modern conceptions of

inertia and acceleration by a smooth process of transition ana

expansion, but it did provide a more convenient, and more

adaptable, starting point than the ideas expressed in Aristotle's

Physics. Galileo's achievements are more properly measured bycomparing his own science of dynamics not with the absurdities

he discovered in Aristotle, but with the theory of impetus whichwas already well formed.

Since it had been handled by Oresme in the fourteenth centurythis theory had made little progress up to the time of Galileo.

Remaining a somewhat specialist complexity, it had not sunk to

the popular level of exposition, but it was taught by respectablemathematicians and philosophers, including Cardano (1501-76),

Tartaglia, Benedetti and Bonamico who was Galileo's ownmaster. Tartaglia (1500-57), moreover, succeeded in making a

useful application of the impetus theory to ballistics, and was the

first writer to aim at computing thq ranges of cannon by means of

tables derived from a dynamical theory, in which task Galileo

later was to believe himself successful. After Tartaglia, if not

before, it was at least clear that in this particular respect a

dynamical theory ought to be quantitative, that is it should be

capable of making exact numerical predictions. Many writers

on gunnery, with varying degrees of imagination, continued to

search for this desideratum within the framework of the impetus

theory until well after Galileo had offered a far better one. This

essential sterility of the impetus theory in the sixteenth century is

an important point. Able men failed to derive from it a mathe-matical description of the phenomena of motion, yet failed also


to develop concepts which could take its place. It is not, therefore,

the case either that Galileo's ambition to mathematize dynamicswas something unusual in the contemporary scientific milieu, or

that, once this ambition had been framed, it was easy to mouldthe necessary modern dynamical concepts out of their crude

impetus forebears. Modern dynamics did not spring from a

modified version of the impetus theory: Galileo was compelled to

return once more to the fundamental concepts of motion.

Towards a new Kinematics

The theory of impetus, the living tradition of dynamics in the

sixteenth century, utilized by Galileo himself in his early treatise

On Motion (1592), had the basic function of explaining certain

phenomena. It had not changed the language in which they were

described. While it gave reasons for the continuation of motion bya body after the moving agent was withdrawn, and in particularaccounted for the properties of motion shown by falling bodies

and projectiles, it had not produced more accurate or fertile

definitions of force, velocity, acceleration. In the technical terms

of philosophy it dealt with the "accidents" of motion the

decelerating ascent of a projectile was caused by an "accidental

levity," its accelerating descent by an ''accidental gravity,"demonstrated by its having effects on impact equal to those

caused by a body at rest of much greater weight. Impetus as a

causal factor, responsible for the accidents of free motion, beingthus associated with the categories of Aristotelean dynamics, no

mechanician before Galileo attempted to deny the validity of the

substantial distinction between the two kinds of motion, natural

and violent. Hence great difficulties arose when the attempt wasmade to describe the path of a projectile, for example, since the

two parts of the problem the ascent and the descent were

qualitatively distinct and subject to different considerations.

Further, progress towards a kinematics through this type of

problem was obstructed by the limitation of the impetus theoryto strictly rectilinear motion. Though both Leonardo and

Tartaglia in the sixteenth century represented the trajectory of a

projectile as a continuous curve, this was no more than a pictorial

device, since their common theory of motion allowed no com-

pounding of natural and violent. In theory the categories of


motion were exclusive, and rectilinear-natural motion could onlyoccur after the rectilinear-violent was completed. Again, if the

relations between the impetus theory and the later concept of

inertia are examined, it is clear that while in isolated statements

exponents of this theory seem to anticipate the rigorous definition

of inertia, in the full physical context their interpretation of the

phenomena was different. For it was not supposed that a body,having acquired an impetus to motion, wouldContinue tojnqveat a uniform velocity. The resistance of the medium ensured that

it would slow down and come to rest; and motion in a vacuous

space was inconceivable when the universe was regarded as a_

plenum. Impetus was like heat, an evanescent accident of matter,of its own nature wasting away. As before, thought on the appli-cation of these ideas to the special problem of projectiles wasmisled by utter deficiency of observation and description. The

impetus mechanicians universally believed that the velocity of a

projectile increased for a space after it had parted company with

the propel!ant^ so that in some strange way its impetus was

actually increased during a part of its free motion. Here also the

theory, instead of leading to universally valid concepts of inertia

and acceleration, required the formation of a special case.

If the scientific tradition inherited by Galileo did not offer anysimple, universal axioms in dynamics, and in its preoccupationwith causation had neglected accuracy in description, it did

provide a suitable mathematical analysis for dealing with changingquantities, such as the velocity of an accelerated body. It is a

matter of historical record that the geometrization of motion, the

establishment of a formula connecting velocity, time and distance

appropriate to the motion of an accelerated body such as a freely

falling mass, was more easily accomplished than the developmentof a framework of kinematics within which such a formula wouldbe not merely possible but inevitable; the formulation of a true

dynamics involved a still greater effort which was hardly com-

pleted before the eighteenth century. The effect of supposing a

uniform (linear) variation in the intensity of a quality, such as

heat, had been studied by a number of philosophers in the

fourteenth century. They found that the second variable (e.g.

heat) could be related either arithmetically or geometrically to

the first variable (e.g. time). Oresme, for example, had demon-strated that if a quality be supposed to vary uniformly from the

THE ATTACK ON TRADITION: MECHANICS 8*

magnitude represented by the line AB to zero at G (Fig. 5), the first

variable being represented by the line AC, this varying quality is

equal in effect to a uniform quality of

the magnitude |AB, since the area of

the triangle ABC is equal to JAB. AC.He expressly stated that if the varying

quality were velocity, the equivalentuniform velocity would be that

attained at the mid-point in time (i.e., ^if AC represents time, of magnitude ^ ^ Geometrical analysis ^AB) and deduced that any uniformly uniformly varying qualities.

varying quality (or velocity) could be

equated to a uniform quality (or velocity). Somewhat earlier

another master of the University of Paris, Albert of Saxony, hadtried to prove that the motion of a freely falling body could be

treated in this way; he had taught that (i) such a body is uniformly

accelerated, and (ii) that in uniform acceleration the instantaneous

velocity is directly proportional to a first variable which is either

the time elapsed or the distance traversed.

The first of these propositions was supported, from Albert's

time to that of Galileo, by reference to the theory of impetus. It

was asserted that the continually increasing speed of a falling

body was caused by the addition, to the impetus already acquired

by it at any point in its descent, of the constant tendency (conatus)

towards the attainment of its natural place which it always

possessed. If this conatus were suddenly abolished while the bodywas actually falling, its impetus would nevertheless bring it downto the ground at a nearly constant speed, but as this conatus acted

as a cause of motion on a body already in motion, it made it moveever faster. By an intuitive process, rather than by strict reasoning,it was argued that the increase of velocity is linear;

1 an argu-ment not approved by all philosophers. It was not accepted byGalileo in 1592, for it might be that the rate of increase wouldslacken as the falling body moved more quickly.The second proposition, or rather pair of alternative proposi-

tions, involved even more obvious difficulties. In the first place,1

Intuitive, because Albert's proposition really implies the true law of

inertia, which he did not enunciate, and also because it is untrue when the

descent occurs in a resisting medium, such as the air. Nor was it logicallycertain that the conatus would act in the same way on a body in motion, as onone at rest.

8a THE SCIENTIFIC REVOLUTION

the notion of instantaneous velocity was very imperfectly graspedno term existed to describe it for while the calculus of varying

qualities could equate these, over a given range, with uniform

qualities, it did not deal with the instantaneous magnitude of the

changing quantity. Moreover even problems on simple linear

relations involve integration, and it was by no means easy to

decide what the integral (the area ABC in Oresme's demonstra-

tion) actually represented. To Oresme it was the total quantityof a quality over a given range, expressed as a simple product

(P * #)> Dut whereas this meaning could be applied to a qualitysuch as heat, it was hardly applicable to velocity,

1 What is the

"total quantity of a velocity"? In either version of Albert's

second proposition, when the calculus of varying qualities was

applied, this mysterious quantity appeared, but the three useful

terms time, velocity and distance could not be brought to

appear together. The difficulty can be explained, of course, in

modern terms by realizing that the product (\vt] or (^vs) cannot

possibly represent any "quantity of velocity." Galileo was the

first to demonstrate this, by showing that the integral is a measure

of the distance traversed. There was no question here of a purely

mathematical difficulty Galileo's geometry is exactly that of

Oresme he succeeded by attaching correct conceptual signifi-

cance to the mathematical quantities.2 Thus his originality was

not so much in making a particular calculation, as in interpretingthe answer once he had obtained it.

Finally, the philosophers who followed Albert had to decide

between the alternatives in his second proposition. Was the first

variable time or distance? This was the principal obstacle to

progress in the sixteenth century within the framework of the

impetus theory. And it was so, not because a choice could not be

made, but because it was not even clear that a choice was neces-

sary. Leonardo typified the confusion of thought in his completely

1 This assumes, for example, that a hot iron having a temperature ft falling

to /2 over time T melts as much ice in that time as an identical iron of constant

temperature J(^ -f /2). It was only much later that Black cleared up the

confusion between temperature and quantity of heat, analogous to the con-fusion in mechanics here discussed.

9 His geometry was equivalent to the derivation of the integral ( Jj/2)from

the differential equation ,= at. He realized, correctly, that this represented

the distance traversed.


clear, and completely incompatible, statements in different

passages of his note-books that the velocity of a falling body at

any instant is proportional to the distance fallen, and to the time

elapsed. For the writers on kinematics who preceded Galileo,

what he was to call the supreme affinity between time and motion

was inevitably obscured. They could not measure small time-

intervals. They most naturally stated the problem whose solution

they sought in a form which made time a function of distance,

that is: "If a stone falls x feet in one second, how long will it take

to fall 100 feet?" Even in making experiments on droppingbodies from different heights, it was more natural to think of

the greater velocity as a function of the greater elevation. It

seemed that the lifting of the stone to a greater height was the

direct cause of its greater velocity on reaching the ground. This

confusion of hypotheses was indeed to trouble Galileo himself,

and some of his brilliant contemporaries. Only one philosopher of

the sixteenth century steered his way unambiguously through it.

This was a Spanish theologian, Dominico Soto, whose commentaryon Aristotle's Physics, fully in the tradition of Oresme and Albert

of Saxony, was published in 1545. After defining "uniform

difform" motion (i.e. uniformly accelerated motion) not

velocity -as proportional to time, he declared that this kind of

motion was proper to freely falling bodies and to projectiles.1 He

did not, however, prove these propositions nor did he suggest a

formula relating time, velocity and distance.2Though he gave

the definition and application of acceleration correctly, he was

still far from a true kinematics, and his propositions were still

dubiously derived from the concept of impetus. If they were

significant, but limited, anticipations of Galileo's theories on

motion, they were also nothing more than one version of Albert

of Saxony's propositions. And there was no further advance. It

was left to Galileo to perform two functions of highest importance:to formulate new, clear concepts of motion, and to derive from

them the complete elements of kinematics, using the fragments

provided by those who had shaped his intellectual inheritance.

1 Cf. P. Duhem: Sludes sur Ltonard de Vinci (Paris, 1906-13), vol. Ill,

pp. 267-95, 555-62.

*i.e., though Soto loosely gives the equivalent of ; at, he did not attempt

to integrate this equation. As will be seen, this was a task that defeated Des-

cartes, and (at first) Galileo.


The Law of Acceleration

During more than two centuries before Galileo's birth the

application of the calculus of varying qualities to the concept of

impetus promised the discovery of the law of acceleration or

rather of two such laws.1 Dominico Soto had decided correctlythat acceleration was a rate of change of motion (velocity) in

time. He had even struck a blow at the dichotomy of natural andviolent motion by deducing that in the violent motion of ascent

the acceleration is negative. Although Galileo's great achievement

was to be in the mathematical analysis of motion, it was not his

first preoccupation. Instead, in his treatise On Motion of 1532, he

examined the physical nature of acceleration, and criticized the

ppimons commonly derived from the concept of impetus. In the

physical sense, he maintained, acceleration was a mere illusion .

His argument at this stage denied the proposition which becameone of the axioms of modern dynamics a constant force gives a

body a constant acceleration for he argued that since the cause

of the natural motion of a body is its weight, each must have a

natural velocity proportional to its weight. He explained the

appearance of changing speed in this way: suppose a heavy mass

projected upwards, the impetus conferred being greater than the

natural conatus to descend. It will rise until the tendency to fall

and the impetus are of equal strength. At this point the body still

possesses a certain degree of impetus and consequently as it beginsto fall back it will increase its speed until all the impetus has

disappeared; after this its motion will have the constant velocity

proper to its weight. In the case of a body falling from rest, he

declared, the impetus acquired by its displacement from the

centre was preserved and the same explanation held.2

Certainly this novel modification of impetus mechanics one

enforced by allowing notions of the causal functions of impetus to

prevail over its usefulness in kinematics introduced no remark-

able clarity. It may be that Galileo's somewhat unfruitful specula-tions along these lines had the effect of turning his thoughts in

1 The law relating instantaneous velocity to distance traversed ( ,=

as]

makes 5 an exponential function. It was therefore beyond the mathematical

competence of Galileo's age.* This theory is discussed in detail by A. Koyre": Etudes GaliUennes (Paris,

1939), PP- 59-64-


a new direction. The followers of Oresrne and Albert had longabandoned the idea that the speed of a falling body is proportionalto its natural weight, though they did not conclude, as did Galileo

later, that in a vacuum all bodies would fall at the same velocity.

Oresme, for example, opposing Aristotle, held that the uniform

velocity of a body is not proportional directly to the "puissance"

applied (e.g. its weight), but to the ratio between the "puissance*'and the resistance to be overcome. He recognized also that the

natural weight of a body is unaffected by its motion; the only

change is in apparent or effective weight, and it is to this (at anyinstant) that the velocity is proportional.

1Moreover, Oresme

accepted the fact that acceleration may continue indefinitely,

and thus differed in principle from Galileo who assumed in 1592that the velocity of a falling body tends towards a uniform value. 2

But it is true that the identification of impetus with accidental

gravity involved conceptual inconveniences which Galileo had

correctly appreciated, though he set them into an outmodedAristotelean pattern.The first evidence of a najor success already shows that Galileo

had turned from a physical-causal to a kinematical approach. In

1604 he wrote, in a famous letter to Paolo Sarpi, that on the basis

of an axiom sufficiently obvious and natural he had proved that

the spaces passed over by a falling body are as the squares of the

times. The axiom adopted was that the instantaneous velocity is

proportional to the distance traversed; an axiom already rejected

by Dornintco Soto. The demonstration of this impossible con-

clusion (which happens to survive)3 made use of the medieval

calculus of varying qualities. Galileo decided that the integral

(area ABC in Fig. 5, Oresme's "quantity of velocity") representedthe space traversed; but the process by which he derived this

integral from his axiomatic function was entirely false. His

reasoning assumed, in fact, that velocity was plotted against time,

not against distance.4 Thus the familiar theorem, s = trta

,was

first derived by Galileo in a process mathematically correct but

vitiated by a conceptual error. Perhaps the theorem was first

tested about this time by the experiment of rolling a brass ball

1 Oresme, Medieval Studies, vol. Ill, pp. 230-1; vol. V, pp. 179-^80.* In the Discourses Galileo explains that the resistance of the air tends to

limit the velocity of a falling body to a maximum value.8 Cf. Opere (Edizione Nazionale), vol. VIII, p. 373.* Duhem: Etudes sur Uonardde Vinci, vol. Ill, pp. 565-6; Koyre*, op. cit.

y p. 98.


down an inclined plane described in the Discourses. 1 It is certain,

at least, that from this time Galileo was convinced of its accuracyas a mathematical description ofthe motion of freely falling bodies.

In Galileo's scientific method experiments were designed to

give ocular confirmation of reasoning; therefore he could not be

satisfied with his newly discovered theorem as a merely empiricalfact. At this point he was most concerned to prove that his axiom

the false law of acceleration followed logically from an analysis

of the nature of motion, and to establish it as a reasoned premiss.2

Could it be justified in philosophy? In tackling this question he

must have been aided by the progress of his thought since 1592,

of which unfortunately little is known. Probably he had already

gone far in renouncing that concern for the causation of pheno-mena shown in his early writing after realizing the confusion into

which it plunged dynamics. In the later phases of his thought

impetus was no longer appealed to as a causal factor but becamea mathematical quantity the product of weight and velocity. As

Galileo's problem became more purely kinematical, he acceptedthe facts of gravitation and the fall of heavy bodies without

trying to impose an explanation, although, from his favourable

references to William Gilbert after 1600, it may be presumed that

he approved the notion of gravity as a quasi-magnetic attraction.3

Already in 1604 he saw acceleration as a fact to be defined, not

explained; but it was not until afterwards that he was satisfied

that the constant effect produced by the constant cause, a force,

is not a velocity but a rate of change of velocity and so resolved

the paradox he had treated very differently in 1592.With the abandonment of the impetus causation of acceleration

is involved the transformation of this vague conception into the

law of inertia. Mach insisted, logically, that this law is the special

case of the law of acceleration where the force applied is nil, andtherefore no separate statement of it is strictly necessary.

4 His

argument is just, but not historical. Historically the special case

was more readily understood than the general law. It was derived

1Dialogues concerning Two New Sciences, trans, by H. Crew and A. de Salvio

(New York, 1 9 1 4) , pp. 1 78-9.2 The empiricist would have derived the law of acceleration mathematically

from the law of distances verified by experiment; but this was not Galileo's

method.8

Dialogues on the Two Chief Systems of the World, pp. 426 et seq.4 Ernst Mach: Science of Mechanics (Chicago, 1907), pp. 142-3.


from the consideration of motion in a resisting medium: if the

impetus c)fa bpdyjs expended in overcoming the resistance, then

in thcf absen^joj>esistance its impetu3nd~velojclty^will rcma^ip

eternally constant. Jj: is in this way thatTJalileo explains the lawof inerHaT in his Discourses, and the non-resisted motion of the

celestial spheres had long been described as a peculiar instance of

undiminished impetus, or inertial rotation. The geometrization of

space, the transference of the phenomena of motion from the real

world of resisting media to an imaginary vacuous space (in which

Galileo had been partially anticipated by Benedetti) and the

restriction of impetus to a kinematic sense virtually necessitated

the transformation of the traditional idea of continued motion

into the idea of inertia, which marks the complete downfall of the

ancient attitude that it is motion, and not rest, which requires

particular explanation in face of the modern notion that only

changes of motion require explanation. In Oresme's natural

philosophy impetus, the motive virtue, had been inevitably a

failing "puissance'*; Galilean kinematics required that inertial

motion be uniform because the reason for its retardation had been

removed. The statement of the law of inertia was indeed fore-

shadowed in the treatise On Motion, where Galileo discussed the

motion of a sphere rolling on an infinite horizontal plane, a

motion which is neither violent nor natural and therefore can be

the result of the action of an infinitely small force; or where he

showed that from the abolition of resistance, as in a vacuum, it

did not follow that movement would be infinitely swift. And if,

in such inertial motion, the causal-impetus was conserved, whatcould be its function when there was no longer a resistance to

overcome? At this point the conservation of impetus becameredundant: it was only necessary to speak of the conservation ot

velocity and momentum. 1

Once the vague concept of impetus had been analysed into two

rigorous statements embodying the law of inertia and a defini-

tion of momentum, the potentialities of the geometric method in

kinematics were vastly extended. With the further addition of an

arbitrary law of acceleration the fundamental theoretical structure

of kinematics was almost complete, and at once the distinction

between "natural" and "violent" motion appeared as an unneces-

sary hindrance. The terms were still used by Galileo, but purely1Koyr6, op. cit., pp. 71, 93.


for classification, without any causal or dynamical significance.

Natural motion had become, by definition, accelerated motion

in accordance with the normal law: the violent, a motion retarded

in accordance with the same law of opposite sign. Gravitation hadbecome a force like any other, which might be greater or less than

other forces opposed to it, and the effect of a force was to accelerate

or retard a body whose only physical properties were weight

(which Newton made, more properly, mass) and inertia. Privi-

leged directions with respect to the centre of the universe, intrinsic

lightness and heaviness, causal distinctions between enforced and

unenforced movements, all disappeared once the aptitude of the

law of inertia in perfectly geometrical vacuous space, where all

planes are infinite, all perpendiculars are parallel, and only simpleforces operate, was realized.

It need not be supposed that Galileo had, by 1604, reached the

stage where the distinction between the essence and the accidents

of motion for which he had sought so long, and which was essential

for the elucidation of the true laws of kinematics, was perfectly

clear in his thought. Rather, his erroneous definition of accelera-

tion at that time, together with the imperfect conception of

inertia which he was never to amend, prove that the steps in the

process of reasoning he had followed still lacked clarity and

rigour. Having abandoned the traditional theory of impetusGalileo's intuition had brought the laws of kinematics almost

within his grasp, at a time when his analysis of the nature of motion

was still far from impeccable. The more adequate reasoning of

the Discourses was to be developed over the next thirty years, yeteven so the ultimate confutation of the false law of acceleration

adopted in 1604 rests upon a paralogism.1 Powerful and original

as Galileo's thinking already was, and close as it came to the

essential idea of motion, his kinematics of Euclidean space was

still a no more complete theory than impetus dynamics. The false

law of acceleration stated by impetus mechanicians still seemed

plausible, and Galileo was still ignorant of the true law, explicitly

stated by Dominico Soto. Galileo had not yet appreciated the

crucial importance of the distinction between the two possible1 This was given in the Discourses (Crew and Salvio, op. m., pp. 167-9),

where Galileo used Oresme's calculus of varying qualities to prove that a bodyfalls any distance s in the same time if this law of acceleration is adopted. Butthis calculus assumed that the variation in velocity was relative to time, andis therefore quite inappropriate.


hypotheses; an ancient train of thought (strengthened by his

geometrical proclivities) bound him to spatial relations. Was his

statement of the distance fallen as a function of time thus a happyaccident which owes nothing, logically, to the progress of his

ideas after 1592, since the axiom of 1604 was available to himthen? Only in a qualified sense. It is true that the geometricmethod of Galileo in 1604 was an attempt to integrate instan-

taneous velocities in Oresme's graphic representation, but

Galileo's calculation is purely kinematical. It is not bound in

terms of explanation to the impetus theory. The quantitativeresult could have been obtained in 1592, but it would have

belonged to a different pattern. Secondly, the error which

enabled Galileo to derive a correct function from a false axiomwas not an accidental error. It was probably inevitable that it

would be made by anyone at that stage of thought attemptingthe same calculation.

Actually, the identical error was made in precisely the samefashion independently by Descartes ana the Dutch physicist

Isaac Beeckman. 1 Their acquaintance began in 16*8, whenBeeckman was already convinced of the perfect conservation of

motion: 'quod semel movetur semper eo modo movetur dum abextrinseco impediatur.' He also believed (following Gilbert) that

gravitation was the result of the earth's attractive force. Accord-

ing to Descartes, Beeckman proposed the following problem:'A stone falls from A to B in one hour; it is perpetually attracted

by the earth with the same force, without losing any of the

velocity impressed upon it by the previous attraction. He is

of the opinion that in a vacuum that which moves will move

always^ ,and asks what space will be traversed in any given time.'

Offering certain dynamical axioms, therefore, Beeckman asked

Descartes to furnish him with a mathematical function relating

time and distance. And Descartes replied with a geometricalconstruction from which he asserted that if the spaces fallen are as

At / 4. \2

/ 4. \3

s, 2J, 45, 8ur, etc., the times of fall are as /, ,

(

jt, (

j/, etc. 2

When his demonstration of this function is examined it is

1 The story of thcii collaboration is told by Duhem in Etudes sur Leonard de

Vinci, vol. HI, by G. Milhaud in Descartes Savant (Paris, 1920) and by A.

Koyre", op. cit., pp. 99-128.2By Galileo's theorem they are of course <, A/a/, a/, aVaf, etc.


apparent that Descartes has done exactly as Galileo did taken

the instantaneous velocity as proportional to the distance fallen,

and arrived at a law of acceleration by a process of integration of

these instantaneous velocities which is as mistaken as Galileo's in

1604. Beeckman's interpretation of Descartes' geometry is even

more curious. For Beeckman wrote out a perfect demonstration

that, from his hypotheses of motion, the instantaneous velocity is

proportional to the time, and the distance fallen to the square of

the time, without ever perceiving that it was different from that

given to him by Descartes, in fact he noted this proof as devised

by Descartes. Evidently neither Beeckman nor Descartes was able

to make a clear distinction between the two laws of acceleration:

neither was capable of seeing that the true function relating

distance and time can only be deduced from the one hypothesis.

Thus the investigations of Beeckman, Descartes and Galileo show

the same intellectual difficulty: even when the essence of motion

was justly apprehended in physical terms, its geometrical expres-

sion defeated their initial efforts. The disentanglement of the

velocity-time and the velocity-distance relationship was still

hazardous and the sheer mathematical task of integrating

changing quantities could not be attempted with any assurance

of success.

There is evidence to suggest that Galileo had developed the

correct formulation of acceleration by 1609, but the steps he

followed are unknown. It may have been that first he discovered

the error of his calculation, and so was led to substitute the true

axiom for the false: but it would seem more likely that it was in

meditating further upon the foundation of the law of acceleration

in his essential idea of motion that he realized the 'intimate

relationship between time and motion.' 1 It is doubtful if the

purely mathematical error would have been apparent to him with

any clarity (since he repeated the same kind of error in his ownconfutation of his first axiom), whereas he may have reflected

that velocity and rate of change of velocity may be conceived as

changes in time irrespective of spatial considerations. Yet if

Galileo had worked backwards from the relation s = lat2

,as he

represented it geometrically (Fig. 6), he may have seen that the

areas ABC, ADE, can only represent distances (\v) because of

their relative dimensions, and that therefore the dimensions AB,1 Crew and Salvio, op. /., p. 16 1.

THE ATTACK ON TRADITION: MECHANICS

A _ u . . /, . _, /AD\ 2

AD must be in time I being such moreover that ( 1=

S*3

ADEN)

It may be, indeed, that if the function s = \aP is assumed to be

true, it is easier to deduce the true conceptionof acceleration, than it is to perform the

inverse and more logical operation (in which

Descartes and Beeckman failed). At all

events, Galileo inserted into the Discourses a

long passage to the intent that the "natural"

idea of velocity is a rate of change in time,

and acceleration therefore a rate of change of

velocity in time, which was written, perhaps,in 1609, and followed this by the exposure of

the reductio ad absurdum in the alternative pro-

position. What he did not do was to derive the

definition of uniform acceleration from the

action of a constant force: though again it

may be conjectured that Galileo's, and

Beeckman's, progress towards this definition

may have been influenced by Gilbert's

suggestion of gravitation as attraction a

suggestion which from the causal point of

view liberates natural acceleration from spatial considerations.

The law of acceleration and the theorem s = \afi derived from

it are the foundations of dynamics, and dynamics exercised a

preponderant influence in the evolution of scientific method

during the seventeenth century. It is no exaggeration to describe

this double discovery, with all the new structure of thought of

which it was the crowning achievement, as the justification of the

new philosophy, as the beginnings of exact science which con-

sciously set itself to proceed by other ways than those of the past,

and which hardly doubted that all the past philosophy of nature

was vain. Yet the law of acceleration had been discussed since the

fourteenth century, and was defined, admittedly not impeccably,

by da Vinci and Soto among the more immediate predecessors of

Galileo. Was the extent of his achievement, then, no more than to

effect the proper integration which would give the law of distances?

If this had been all, it would have been a great feat, for the

perplexities of Descartes and Beeckman show that the law of

acceleration did not prove a ready key even to the most acute and

D Velocity*

FIG. 6. Time, velocityand distance.


resourceful of his contemporaries. But this was not all; Galileo,

a less ingenious mathematician, excelled Descartes in a mathe-

matical problem because he understood the conceptual structure

into which the key would fit. In fact the single law of acceleration,

set in the framework of impetus theory, had hardly proved more

useful in the sixteenth century than the crude observation that

falling bodies travel more quickly as they approach the earth. Its

full significance was revealed only when Galileo applied it in a

context of dynamical theory in which the law of inertia had

replaced the idea of impetus, a theory so highly abstracted that

causation, friction, resistance, were no longer considered as

relevant. To Galileo the law was no longer a descriptive deduction

from physical principles (as it was to Soto), or an arbitrary

assumption (as it was to Descartes) but a primary fact, inevitable

in theory and confirmed by experiment. There are many similar

instances in the history of science of the isolated statement of an

anterior phase becoming the core of a comprehensive generaliza-

tion; so comprehensive, in this case, that Galileo obtained from it

knov/ledge of a whole class of mechanical theories. It is the com-

bined effect of this rapid evolution in thought, requiring clarity

of definition and elaboration of mathematical expression, the

re-thinking of the nature of motion and the statement offunctions

making quantitative calculations possible, that determines the

magnitude of Galileo's achievement. The commentary uponAristotle's physics had been replaced by the mathematical

scaffolding of a new branch of science.

Galileo and Descartes

The strategic lines of the Discourses on Two New Sciences were

probably sketched out about 1609. The origins of the earlier

dialogues, in which Galileo discussed cohesion and disputedthe doctrine that

"nature abhors a vacuum," attacked the

Aristotelean view of the accidentals of motion (that there are

absolutely light bodies, that velocity is proportional to weight,

etc.) and began the study of the strength of materials (the other

"new science") may be traced to a period more than ten years

earlier, when Galileo, in his most Archimedean manner, was

introducing into wider fields the principles of the sciences of

statics and hydrostatics founded by his favourite Greek author.

Certainly the secret of the trajectory of a projectile was known


to Galileo by 1609, ofwhich he wrote later, 'truly my first purpose,which moved me to speculate on motion, was the discovery of

such a line (which most certainly when found is of little difficulty

in demonstration); nevertheless I, who have proved it, know what

pains I had in discovering that conclusion.' 1 The theory of pro-

jectiles, the propositions relating to the oscillations of a pendulumby which Galileo established its isochronous property, and the

various theorems depending on the principle of the conservation

of vis viva (momentum) are all straightforward deductions from

the complementary laws of acceleration and inertia. Fragmentsof this reasoning had been used by Galileo in earlier years; for

example, the experiment of rolling a ball down an inclined planeassumes the conservation of motion or vis viva. Now the whole was

welded into a single coherent mathematical structure. It was not

a faultless structure, for a number of Galileo's minor theorems were

later found to be false, but its foundations were sound.

With one important exception, the theory of impact and the

partition of kinetic energy between colliding bodies, the whole of

seventeenth-century kinematics springs from Galileo's Discourses.

\Vhen, finally, this became the instrument by which Gilbert's

conception of attractive forces could be interpreted mathe-

matically, the classical theory of dynamics was created. But if the

lines of descent are direct, the historical process was complex.Galileo's intellectual evolution was by no means unique, thoughit has chronological priority. An independent "modern" tradition

in dynamics can be traced to the fertile conjunction of Descartes

and Isaac Beeckman. Other \vriters also, less strikingly, demon-strate a general tendency for the idea of the conservation of

impetus to be transformed into the conservation of motion. As has

so often happened in science, the decisive advance was made byone man in accordance with a broad progressive movement.

Moreover, the reaction to the publication of Galileo's dis-

coveries in 1632 was not simply favourable or adverse. 2 In the

later seventeenth century the mathematico-mechanical group of

scientists, the true heirs of Galileo, confided entirely in the essen-

tial conception of motion developed in the Discourses; in England,1 That is, the trajectory according to the usual assumptions of Galilean

kinematics, in a vacuous, perfectly Euclidean space. Cf. Opere, Ediz. Naz.,vol. X, p. 229, vol. XIV, p. 386.

2 The elements of kinematics were indicated in the Dialogues, though a full

discussion waited for the Discourses of 1638. See below, p. no.


however, where this group was very strong and produced the

dominating figure of Newton, the Galilean tradition was partlymodified by the companion influence of Francis Bacon in the

direction of more forthright empiricism. Thus Newton completed

fhe mathemfltization of the distinction between the ideal laws

cf mntinnrand the real motions of terrestrial bodies. The repre-

sentatives of conservative, anti-Copernican science, such as

Giovanbattista Riccioli, after a vain attempt to dispose of the

Discourses altogether, ultimately accepted the law of acceleration

as a rough empirical truth, a mathematical hypothesis approxi-

mately agreeing with actual experiments, but continued to opposethe philosophy of motion from which this law was derived. This

attitude was not dissimilar to that adopted by Tycho Brahe with

regard to Copernicus: the innovations could not be philosophically

true, but they could, by twisting them a little, be taken as

quantitatively reliable. Far more important for the developmentof science was the position of the Cartesians, who likewise acceptedGalileo's law of acceleration as a quantitative statement, while

opposing Galileo's ratiocination in philosophy.Descartes himself would never allow any supreme merit to

Galileo as a scientist, and in his later utterances, after the crisis

of 1619-20 in Descartes' intellectual development, he felt himself

far superior because he alone possessed the true method of

philosophy. In general the reception in France of Galileo's newscience of motion was not uncritical: along with Descartes, neither

Mersenne, nor Fermat, nor Roberval would give completecredence to a natural philosophy which applied such a violent

process of abstraction to the complicated world of experience.For Descartes this objection was insuperable, and he finally cameto regard Galileo as a mere phenomenalist who, lacking insightinto the total mechanism of the universe, had merely been success-

ful in isolated feats of mathematical description. Of the Dialogueson the Two Chief Systems of the World he wrote in 1634 that Galileo

philosophized well enough on the subject of motion, but that verylittle of his doctrine was wholly true. He admitted that Galileo

was more correct when he opposed current notions, and hadindeed expressed some of Descartes' own ideas it is strange to

find him identifying Galileo's theorem, s = \at2,with that which

he had himself devised in 1618. Four years later Descartes'

judgement was more harsh. Although he approved Galileo's


introduction of mathematical reasoning into physical questionsand his criticism of scholastic errors, he added that Galileo hadbuilt without foundation because he did not at all proceed byorder in his investigations, nor consider the first causes of natural

phenomena. The abstraction of Galilean science which has been

its merit in the eyes of many subsequent historians was for

Descartes its cardinal defect. He had now conceived his own modelof the universe, and he found the Galilean model too remote from

reality to be worthy of serious consideration. Its prime requisites,

such as vacuous space and the constancy of gravitational forces,

were assumptions contradicted by a true insight into nature. 1

Descartes was no less convinced of the errors of the past than

Galileo. He was equally a pioneer of the new natural philosophy.But whereas Galileo had arrived at a new method of procedure by

patient inquiry into particular problems so that his essential idea

of motion was the product of the endeavour to resolve the incon-

sistencies in the prevailing conception, Descartes' method taughthim that it was essential to settle the simplest and most generalideas first, and then (as in the three treatises appended to the

Discourse on Method] particular applications could be made to

specific problems. What, for instance, is the simplest idea of

matter? Extension, Descartes replied: matter is that which occu-

pies space. To suppose that space could exist without a material

content, that dimension couid be conceived without any physical

consideration, was meaningless. God could formally create a

vacuum, but so interchangeable were the ideas ofspace and matter

for Descartes that if a vessel was imagined to be divinely exhausted

of matter, it meant only that its walls had been brought togetherso that there was no space between. Of course he admitted that

vessels could be sensibly exhausted of grosser matter, such as

water or air, when they would remain filled with a purer species

capable of passing through the pores in the coarse material of the

vessel. Similarly with motion: the simplest idea was the translation

of a body from one situation among other bodies to another

situation among a different set of bodies, and motion and rest

were simply states of matter. This definition enabled Descartes

to declare formally that the earth does not move, since despite its

1 (Euvres de Descartes, publics par Charles Adam et Paul Tannery, vol. I

(Paris, 1897), pp. 303-5; vol. II (Paris, 1898), pp. 380-8. Also J. F. Scott,

The Scientific Work of Descartes (London, 1952), pp. 161-6.


revolution around the sun in the vortex of the solar system, its

environment in surrounding matter is unchanged. Movement,

properly, was displacement; as a body moves, it is forced to

displace other matter from its path, and a corresponding quantitymust occupy the volume which the motion of the body would

otherwise leave vacant. From these considerations Descartes

deduced more specific laws. In the first Beeckman's conservation

of motion became the perpetuation of the state of matter unless it

is acted upon in some way. In Descartes' second law this principleof inertia was perfected by the statement that all bodies in motion

continue to move in a straight line, again unless they are acted

upon. Thus the necessity for some centripetal lien or force in

circular motion was explicitly recognized by Descartes a funda-

mental contribution to mechanics. The third law of motion was

the fundamental rule for determining the partition of motion

between impacting bodies. It was only later that the mistake in

Descartes' formulation of the laws of impact became significant;

they were, however, essential to the development of his corpuscular

philosophy of matter. The notion of an intangible, incorporeal

force, like Gilbert's attraction, was to Descartes barbarous andunthinkable. The state of matter could only be altered by the

direct action of other matter, that is, by contact between bodies. 1

Hence what appears as the action of an incorporeal force is in

reality the action of a stream of impalpable particles.

Action at a distance such as the gravitational pull of masses

across empty space was to remain for Cartesians the bitter pill

of Newtonian mechanics. Implicitly its impossibility conditioned

Descartes' reaction to Galilean mechanics. When he declared

that Galileo had not inquired what weight is, when he maintained

that Galileo's description of how bodies fall was vitiated by his

ignorance of why they fall, he meant that in nature there are

no constant forces producing constant accelerations. 'That is

repugnant to the laws of Nature, for all natural forces (puissances)

act more or less, as the subject is more or less disposed to receive

their action; and it is certain that a stone is not equally disposedto receive a new motion or an increase of velocity when it is

1 Thus Descartes was led into an insoluble problem the nature of the

contact between the soul (spirit) and the matter of the human body, (Cf. M. H.Pirenne: "Descartes and the Body-Mind Problem in Physiology," Brit. J. forthe Philosophy oj Science, vol. I, 1950.)


already moving very quickly, and when it is moving very slowly.'1

Descartes' reasoning is quite clear. Terrestrial gravity he believed

to be the effect of a stream of corpuscles of impalpable matter

sweeping towards the centre of the earth. As this stream swept

through bodies of ordinary coarse matter, it pressed them likewise

towards the centre. Clearly this pressure would diminish with the

increasing velocity of the falling body, which would tend towards

a limit, the velocity of the stream itself.

In 1618, under the influence ofBeeckman, Descartes had treated

motion as a geometer, and had made the same sort of mistakes as

Galileo in 1604. In later years, at the time when Galileo's treatises

were published, he thought of motion in the context of physicalor cosmological theory. Unfortunately, as he penetrated from the

level of description to the deeper level of explanation, Descartes

denied himself the possibility of mathematizing the law of

acceleration: the mechanism, as he framed it, contained too manyunknown variables. 2 The work in which his system of nature is

expounded, The Principles of Philosophy (1644), is in fact almost

completely non-mathematical, although Descartes is one of the

greatest figures in the history of pure mathematics. For all the

originality of its starting point, this was a synthetic system,

blending harmoniously elements derived from the animistic

science of Aristotle with others taken from the mechanistic

philosophy of Democritus and Epicurus; and, like these earlydeductive philosophers, Descartes was inevitably preoccupiedwith the uncovering of chains of causation, starting from his

initial postulates concerning the nature of the physical world.

When by deductive reasoning the end of the chain was reached,it was impossible to adopt the reverse process of analysis and

abstraction which alone makes a mathematical science possible.

Therefore Cartesian mechanics could never consist of n*ore than

general principles and the false laws of impact. Therefore also

Descartes could never do more than admit that Galilean kine-

matics gave a rough approximation to the real dynamics of the

world of experience.In Descartes the dichotomy between the mathematical and the

physical attitudes to nature is almost complete, since he could not

1 Adam and Tannery, op. '/., vol. I, p. 380.8Koyre, op. '/., pp. 126-7; Paul Tannery: Mtmoins Scientifiques, vol. VI

(Paris, 1926), pp. 305-19.


sacrifice causation to computation. The Cartesians of later genera-tions were more eclectic and less rigorous. They could not resist

the intellectual charms of Descartes' discoveries both in puremathematics and in natural philosophy. In attempting to combine

them they became the illegitimate heirs of Galileo. Havingrealized the futility of seeking directly for the descriptive dynami-cal laws of the actual universe, they sought instead for the correc-

tion which ought to be applied to the ideal laws of Galileo in order

to apply them to a world where bodies move in resisting mediumsand there are no pure forces. No tradition is perpetuated un-

adulterated and the later Cartesians compromised with the pheno-menalism which Descartes had condemned. While they firmlymaintained his method of philosophizing, his theory of the origin

of the universe, of the corpuscular mechanisms involved in the

phenomena of light and vision, magnetism and electricity, gravityand the planetary revolutions (none of which, from its very

nature, could be subjected to direct empirical verification), in

discussing any problem of mechanical science descriptively theyturned to the mathematical model of Galileo, to which there wasno alternative. There was a subtle change of perspective: instead

of proceeding from indubitable first principles to the details of

nature and the ultimate descriptive mathematical understanding,as Descartes had sought to do, later Cartesian scientists followed

a different path, that of working out the modifications requiredin transposing a problem from a mathematical model to the

natural scene.

This is most true of the Dutch physicist, Christiaan Huygens,for many years the mainstay of the French Academic des Sciences.

Certainly Huygens, when still a boy, had worked out a purelymathematical proof of Galileo's law of acceleration, and certainlyin full age he confessed that his thoughts had been too greatlyinfluenced by Cartesian fictions. But it is also clear that he could

never have become an entire phenomenalist : he was too greata Cartesian to be a Newtonian. He has been appropriately con-

sidered in relation to the Cartesian tradition. 1 Much of Huygens'work was suggested by Descartes' own original thoughts (for ex-

ample, his study of centripetal forces and the laws of impact),much of his basic theory was Cartesian. Always denying the reality

1e.g. by P. Mouy: La Dlvtloppement de la Physique Cartesienne (Paris, 1934),

chap. II.


of a physical vacuum, he believed in impalpable matter or aether,

and his theory of gravity was wholly in agreement with Descartes'.

He was never converted to "action at a distance." Yet his particu-lar investigations are in the highest class of seventeenth-centurymathematical physics, and as an experimenter also Huygens, with

his strong affiliation to the Royal Society of London, was not

negligible. In the actual conduct of his scientific career no one

was more justly an exponent of the Galilean tradition in science

than Huygens who, like Galileo, allied astronomy and physics.

Only on the widest issues did he fall below the example whichGalileo had set, when as it seems, measuring the mathematical

model against the physical model of Descartes, he found his

attachment to the latter unbreakable. The Cartesian mechanical

theory of causation in nature was inevitably the frame of reference

for each of his researches, deeply though his spirit as an inquirerwas akin to that of Galileo.

The example of Huygens sufficiently demonstrates the com-

plexity of intellectual inheritance in the second half of the century.There was no simple antithesis, uniform at all points, between

conventional science and the new philosophy of the scientific

revolution. There was no pure line of descent in mechanics from

Galileo to Newton, nor among the scientists of the French school

who broadly accepted the framework of Cartesian natural philo-

sophy. The conflict between the Newtonian and the Cartesian

system of the universe which lasted till about 1 740 was indeed

absolute and irreconcilable, but it should not be supposed fromthis that the Cartesians had borrowed nothing from Galileo, nor

that the Newtonians had learnt nothing from Descartes. Much of

the application of mathematics to mechanical problems whichhad been such a fertile arid active field of science during the half-

century between 1638 and 1687 was in fact the work of men whodid not subscribe without reservation to Galileo's philosophy of

science.

In addition, the many lesser contributions to mechanics cannot

be overlooked. Admittedly the main source-books for the later

seventeenth century were the Discourses of Galileo and the Prin-

ciples of Philosophy of Descartes, but other works of the nascent ageof modern science held fruitful suggestion, among them the prac-tical machine-books and even such a curious confection as BaptistaPorta's Natural Magic. Inventive interest in the development of

ioo THE SCIENTIFIC REVOLUTION

new mechanical devices was a prominent feature in the activities

of the early scientific societies, the Academic Royale dcs Sciences

enjoying the privilege of examining theca and officially approvingthose which it found sound and beneficial. Again, though the

progress in statics during the late sixteenth and early seventeenth

centuries was less pregnant with consequence than that in dy-namics there was a profound change in degree rather than a

change in kind this progress too contributed to the methodologyof science as well as to the formation of the whole body of experi-

mental learning. Simon Stevin, whose investigations providedanother part of the foundations of seventeenth-century mechanics,was a man of wide competence litde short of the first rank. In

the history of mathematics he has an important place as, amongother things, one of the leading early exponents of decimal arith-

metic. With another Fleming, De Groot, he carried out, about

1590, an early experiment on the fall of heavy bodies to test

Aristotle's theory of motion. In statics his work on parallel forces

utilized the important principle of virtual velocities or displace-

ment;he recognized (like Galileo) that the equilibrium of a system

of pulleys or levers depends upon the constancy of the productof the weight and the distance moved in each of the balanced

members. Stevin extended the same principle to the action of

non-parallel forces. He showed that unless perpetual motion is

assumed to be possible (and Stevin was one of the first to consider

this ancient fallacy in the light of plain mechanical reason) two

weights resting upon a pair of inversely inclined planes mustbalance when they are proportional to the lengths of the

planes. His demonstrations contain the principle of the triangle of

forces, and therefore the first implication of vector-quantities in

statics, just as Galileo's treatment of the trajectory of a projectile

contains the first use of vectors in dynamics. In hydrostatics he

examined the conditions necessary for the stability of a floating

body, and the distribution of pressure in liquids, involving a prob-lem of integration which he solved successfully. He was the first

discoverer of the so-called'

'hydrostatic" or "Pascal's paradox,"that the pressure of a liquid upon a surface varies only with the

area of the surface and the height of the column of liquid above

it, irrespective of its cross-section. This, along with his other dis-

coveries in mechanics, Stevin described in Flemish in 1586. Isaac

Beeckman noted it there, and drew the attention of Descartes to


this strange phenomenon. Descartes without acknowledging his

source discussed its theory at some length. From Stevin too the

paradox passed to Pascal, who analysed it very completely in

1648.!The essence of mechanistic philosophy in the seventeenth

century was the axiom that all natural phenomena~couTJT:)e re-

duced, by a sufficiently prolonged process of^abstraction^ to one

single kind of changev the motion of matter. This axiom was the

foundation of Cartesian science, and with limitations and qualifi-

cations it was generally shared by scientific men. Descartes' great

contribution to dynamics, in a sense, is that he made it the primaryscience. In so doing he caused research to enter some false paths,but his idea was to be vindicated in the kinetic theory of the

nineteenth century. Galileo provided the elements of kinematics,

the basic conceptualization and the mathematical procedyircs

again further elaborated by Descartes in coordinate geometrywhich rendered definable the properties of matter in motion. For

the next century a major concern of science was the extent to

which nature could be explained broadly in terms of Cartesian

mechanism interpreted with the aid of Galileo's descriptive

analysis of motion.

1Milhaud, op. cit., p. 34.

CHAPTER IV

THE ATTACK ON TRADITION: ASTRONOMY

THEperiod of silence in which comparatively little comment,

favourable or unfavourable, was made on the new celestial

system proposed by Copernicus lasted for about a genera-tion after the publication ofDe Revolutionibus. From the later yearsof the sixteenth century to the middle of the seventeenth there was

a noisy and not invariably elevated dispute between the adherents

of the new and the old opinions in natural philosophy in which

astronomy was the touch-stone of faith. The triumph of the

innovators did not come rapidly, for it is always easy to exaggeratethe adaptability of the scientific intellect. Books were written

assuming the truth of the geostatic system, astronomical clocks

and armillary spheres were constructed to show a motionless

earth, until at least the end of the seventeenth century. And it is

well to remember that though the ascendancy of the "new

philosophy" made modern science possible, the material pointso often at issue was not of long-term importance. It is now recog-nized that before using words like "motion'' and "rest" in rela-

tion to the solar system the frame of reference must be explicitly

defined. It was by no means logically essential to the progress of

astronomy that men should believe the earth to have an annual

rotation around the sun. No phenomenon known to the seven-

teenth century required such a motion for its explanation; in

practical astronomy the relative movement of earth and sun

could be equally well interpreted by supposing either to be at

the centre of the other's orbit. Before the celestial mechanics of

Newton's Prineipia was developed, there was no positive, demon-strative argument that can be called conclusive either way; onlyin the sense that the progress of science demands the liberty to

theorize, to extrapolate beyond the available positive knowledge,is it true that the Copernicans had enlightenment on their

side.

The first conflict between the innovators in philosophy andauthoritarian learning, which was full of consequence in framing

102

THE ATTACK ON TRADITION: ASTRONOMY 103

not only the attitude adopted by the Roman Catholic Churchtowards the great astronomical question but also (in part) the

spirit of the scientific movement, at once defensive against sus-

pected allegations of irreligion and hostile to the older kind of

literary scholarship, had strictly no connection whatever with

natural science. This conflict was exhibited in the famous con-

demnation of Giordano Bruno. Bruno was burnt in 1600 because

he taught the plurality of worlds; he was moreover technically an

apostate from a religious order. He believed that beyond the

universe we observe there are other universes similar to our

own, equally of divine creation, equally inhabited by immortal

souls. Speculation of this kind has a natural fascination for some

minds; it had occurred very early in the history of systematic

thought, and had received the strong disapproval of Aristotle. It

had always been regarded as theologically dangerous. Yet Nicole

Oresmc, in his Livre du del et du Monde gave considerable attention

to it. He envisaged the possibility of a plurality of worlds in time

or in space so that there might be one world enclosed in another

or separate worlds scattered in space, for example beyond "our"

universe, all the work of one creator. Aristotle's argument that

the earth of another world would be drawn to a natural place at

the centre of this he confuted by rejoining that the natural placefor such earth would be at the centre of its own world. The restric-

tion of the divine creative power to the fabrication of one universe

he regarded as a denial of omnipotence. Further, he was bold

enough to declare that it is natural to human understanding to

believe that there is space beyond "our" finite universe; in this

God could bring other universes into existence. From this dis-

cussion Orcsme concluded that reason alone could not eliminate

the possibility of a plurality of worlds, but that in fact there never

had been more than one, and probably there never would be. 1

In the seventeenth century a similar speculation produced the

first scientific fantasies, such as John Wilkins' Discovery of a World

in the Moon (1638).The allied belief in the infinity and eternity of the whole cosmos

was also ancient.Expounded by Lucretius, who had them from

Democritus, these doctrines were further developed by an im-

portant group of Muslim and Hebrew philosophers of the middle

ages, though little favoured by Christians. Oresme seems to hint

1 Medieval Studies, vol. Ill, pp. 233, 242, 244.


at the infinity of space. Nearer to Bruno's own time the impossi-

bility of conceiving a boundary to space was asserted by Nicholas

of Gusa in the fifteenth century: and it was from him that Bruno

received his inspiration. In his own time the idea was specifically

related to the Copeniican hypothesis by the English mathe-

matician Thomas Digges. Digges believed the fixed stars to be

infinitely remote from the earth, a notion he was free to adoptsince it was no longer necessary to suppose them fastened to a

revolving sphere. All that the Copernican hypothesis required,

however, was that the ratio of the distance of the fixed stars to

the earth's distance from the sun should be a large number; hadthis number been far smaller than it actually is, the sixteenth-

century astronomer would still have failed to detect any evidence

of the earth's motion in his celestial observations. As for the

infinity of space outside "our" universe, it was perfectly recon-

cilable with Ptolemaic astronomy and not at all a Copernicaninnovation. However great the interest of Bruno's ideas in them-

selves, the idea of the plurality of worlds was not inspired by the

scientific renaissance, they were not a logical deduction from

heliocentric astronomy, and they were totally irrelevant to the

progress of science. Bruno was not a scientist, and his dispute with

Rome turned on a purely metaphysical problem.It is well to attempt to define the contemporary appreciation

of a situation such as this. That the introduction of religious

considerations into a question of quasi-scientific speculation is

quite distinct from a similar intervention in the interpretation of

observations or experiments was perfectly clear to philosophersof the middle ages and the early modern period alike. A very high

proportion of scientists up to the mid-seventeenth century were

men of unusually profound religious conviction, and none used

science as a lever against religion. Thomas Hobbes won no

countenance from the Royal Society. The furtherance of science

and religion were commonly regarded as inseparable objectives.

The English scientists of the seventeenth century, especially, were

far more complacent than medieval scholastics in their belief that

reason and research properly conducted could never conflict with

religious dogma. The attitude of the middle ages had been that

where reason was incompetent to decide, faith should pronounce:and that in many instances faith must even prevail against reason.

In the period of the scientific revolution natural theology was still


distrusted, and divine modification of the laws of nature in rare

events was a commonplace. A general antithesis between science

and religion was consequently out of the question; a particularantithesis over a single point could only be due to some misinter-

pretation either of nature or of religious truth. Even for the most

empirical of scientists, like Boyle and Nev/ton, the introduction of

religious considerations into the pattern of scientific investigationwas natural and inevitable. They would not have dreamed of

denying the validity of a universal moral or religious law a

concept to them more binding than scientific law. To the Protes-

tant mind of the seventeenth century the judgements upon Bruno,and later Galileo, would seem full of human error and expressiveof the bigotedly narrow outlook of the unreformed Church, but

they would agree that it was the duty of the responsible officers

for the time being to enforce the moral law according to their own

enlightenment.1 No sympathizer with Bruno or Galileo believed

in complete freedom of thought and expression; none wo aid have

asserted that scientific activity and theorizing are completelyoutside the range of universal moral law. For the seventeenth

century the burning of Bruno could not be wholly wrong in

principle as it was to the liberals of the nineteenth. Galileo, thoughhe never surrendered his inner conviction of scientific rectitude,

apparently admitted the right of the ecclesiastical authorities to

pass religious censure upon his arguments. He lived and died in

the Catholic faith; and when compelled to make his formal

recantation, it would seem more reasonable to attribute his

compliance not to lack of courage, but to recognition of the then

universal belief that moral and religious truths are of a higherorder than the scientific. Galileo could only lament that in his

case the moral law had been misapplied.

Although the pronouncements of the Holy Office were not

opposed to any positive scientific knowledge of the time, and in

the case of Bruno only condemned a form of quasi-scientific

speculation, they had a deep effect upon the scientific move-

ment. They were widely interpreted as a final declaration againstthe Copernican system, and there is evidence that some (like

Descartes) who were disposed to favour a heliostatic model were

impelled to express their ideas in veiled and guarded terms. It

seemed as though innovations in natural philosophy must lead to

1 As the reformed Church of Geneva had upon the person of Serveto.

io6 THE SCIENTIFIC REVOLUTION

outbreaks of heretical opinion, as reactionaries had long predicted.

Even in England, critics of the newly founded Royal Society did

not fail to assert that its methods were subversive of the Churchof England. An odium, which had not existed in the early sixteenth

century, was for a time attached to any originality in astronomical

thought. But the challenge provoked a powerful reaction in menlike Galileo and Kepler. It created a situation in which the newdoctrines had to be effectively vindicated; it was no longer

possible for the two systems of the world to exist peacefully side

by side.

The pre-Newtonian development of heliostatic astronomy maybe analysed as involving four principal stepsi Firstly, the dissolu-

tion of the prevailing prejudice against allowing any motion to

the earth, which involved a careful criticism of all existing

cosmological ideas in order to create a new pattern in which

such a motion would no longer seem implausible, and a broad

discrediting of Aristotle's authority. A necessary auxiliary to this

was the most important second step-, in which physical theories

were revised to show the invalidity of objections against the

Copernican hypothesis arising out of terrestrial mechanical

phenomena. Thirdly, the new astronomy was greatly enriched by

qualitative^ observation, which suggested that the old teachingwas very inadequate. Fourthly, exact quantitative observation

provided new materialTTor recalculating the planetary orbits,

thereby leading to the abandonment of the ancient preconceptionin favour of perfect circular motion, and to the enunciation of

new mathematical laws. Kepler's discoveries might have been

expressed in the terms of the geostatic system; but as Kepler was

a staunch Copernican, his whole discussion of the solar system was

constructed in such a way as to give further force to the hcliostatic

hypothesis. The accomplishment of these four steps extended over

a period of roughly half a century (c. 1580-1630), while their

assimilation and particularly the gradual recognition of Kepler'slaws of planetary motion occupied another generation. Duringthe middle period of the seventeenth century the nature of the

problem was again slightly changed under the influence of

Descartes' natural philosophy, which tended to enlarge the dis-

parity between the natural-philosophical and the mathematical-

astronomical approach which the discoveries of the first third of

the century seemed rather to diminish.


The contributions of Galileo to the first three of these steps were

of major importance: to the fourth, quantitative observation, he

brought almost nothing. Galileo was not an astronomer as the

word had previously been understood, he was never interested

in the traditional procedures of positional astronomy, but as a

philosopher he applied new astronomical techniques, mostly of

his own invention, to the examination of cosmological problems.Before 1 609 his studies were very largely, if not wholly, devoted to

physics and mechanics. He must, of course, have been thoroughly

acquainted with elementary astronomy, and it appears that he

had already read Copernicus and become converted to his doc-

trine, which he had at first distrusted. In 1609 Galileo learnt of

the Dutch optical device which made distant objects seem near,

and with this hint and considering the invention as a problem in

optics he constructed his own telescope. During succeeding yearshe endeavoured to increase the magnification of this instrument

and to effect improvements in lens-grinding, besides carrying out

celestial observations which were recorded in a series of treatises. 1

Galileo was the first to appreciate the usefulness of the recentlyinvented telescope in astronomy, and was therefore rewarded bymany discoveries, but within a few years a considerable group hadtaken up qualitative investigation in astronomy. The old and the

new branches of the subject remained practically distinct until

about 1670, when the application of the telescope to measuringinstruments became effective; during Galileo's lifetime astronomywith the telescope brought into being a completely new branch of

scientific investigation. Its first results were striking, and provided

powerful arguments against Aristotle. In January 1610 Galileo

saw four of the satellites of Jupiter, which he called the Mediceanstars and regarded as forming a visible model of the whole solar

system. Later he observed the phases of Venus, from which it

could be deduced that the planet revolves around the sun, andnot between the sun's sphere and the moon's as Ptolemy's hypo-thesis supposed. He observed the moon itself, and confirmed his

conjecture that it was a body resembling the earth, with valleys

and mountains whose heights he estimated from the lengths of

their shadows. His telescope resolved part of the Milky Way into

a dense cluster of stars. The discovery of sun-spots was made by1 Sidcreus Nuncius (

1 6 1 o) ; Istoria e dimostrazioni intorna alU macchie solari (1613);// Saggiatore (1623), and the Dialogues of 1632.

io8 THE SCIENTIFIC REVOLUTION

several observers of whom Galileo was one. They are, of course,

sometimes visible to the naked eye; Kepler had failed to recognizeone in 1607 when seeking for a transit of Mercury. Fabricius

probably made the earliest discovery of these macula,

and Scheiner certainly wrote the largest book on them, but

it was Galileo who realized their importance for astronomical

theory.To anyone who was prepared to think, the discoveries that

followed upon the invention of the telescope would suggest a

single train of thought which was certainly anti-classical but

equally departed very far from the ideas of Copernicus. It would

seem that celestial phenomena were much more complex than anyextant astronomical system allowed. It would seem that the stars

were not finitely or infinitely remote, but distributed through

space. It would appear also that the heavens, far from being in-

corruptible and unchanging, were undergoing regular and irregu-

lar mutations, as Tycho Brahe had suggested as early as 1572.

The planets, notably Saturn, whose ring-satellite was not yet

fully understood, altered their aspects, and the sun itself was

stained by spots that enabled its revolution upon its axis to be

traced. The image of the moon could be conceived as comparableto that of the earth seen at the same distance. All this tended to-

wards one general conclusion, that the universe was a physical

structure, noLjCDmposed of light and a matter totally different

Trorn the matter of the terrestrial region, but rather of two types of

physical body.[The first, the stars, were incandescent sources of

light and plainly physical since they were not invariable. The

second, of which more could be learnt, the planets, were physicalbodies practically indistinguishable at this stage from the earth

itself, which could now be placed without hesitation in the class

of solar satellites on physical grounds as well as by reason of its

motioni Physical astronomy was thus a creation of the telescope,for in the past the sole subject of astronomical science had been the

analysis of the positions and motions of the heavenly bodies with-

out consideration of their nature, which had been resigned to the

speculative discussions of philosophers, while astrology had em-braced the supposed influences of these bodies upon the terrestrial

region. The concept either of physical astronomy or of celestial

mechanics (which came later) was completely irreconcilable with

the philosophic background of sixteenth-century practical astro-


nomy, and it was necessary to reinterpret the Copernican heliostatic

universe in this new light.

This reinterpretation was achieved in Galileo's Dialogues on the

Two ChiefSystems of the World (1632) which was, therefore, far morethan a mere defence of the heliostatic principle. At the same time,

it will be seen that Galileo's treatise did not advance beyond DeRevolutionibus in one respect it retained perfect circular motion

as a"privileged case" and in another respect it was even far

inferior, for as a guide to positional astronomy the Dialogues are

worthless. Galileo wholly neglected the complexities of planetarymotion with which astronomical theoreticians had struggled for

two thousand years, and on which his contemporary Kepler wasto spend his life. In astronomy, Copernicus and Kepler set them-

selves against Ptolemy; Galileo's opponent was Aristotle, the

philosopher.Within a few years after 1609 Galileo's teaching at Pisa as

modified by his discoveries with the telescope had become uncon-

ventional enough to occasion his first encounter with the HolyOffice. The Dialogues were conscious propaganda for the new

philosophy, though the opinions expressed were put in the mouthsof imaginary characters. Galileo did not scruple to indulge in a

certain buffoonery with the Aristotelean Simplicius, whose feeble

defences are mercilessly attacked. The first pages of the Dialogues

contain a delightful battle of wits in which of course the Copernicanis made to score heavily. Galileo examines the reasoning by which

it is argued that the heavens and the terrestrial region are distinct,

both in their motions and their natures.Uie J^QBCdes that the

motions of the heavenly bodies are perfectly circular, since only

by such motion could the pattern of the heavens be preservedwithout change, and that rectilinear motion 'at the most that

can be said for it, is assigned by nature to its bodies, and their

parts, at such time as they shall be out of their proper places,

constituted in a depraved disposition, and for thaCcause needingto be reduced by the shortest way to their natural

state.}1 But he

denies that terrestrial bodies do, in fact, move~ftkmg"Sf?aight lines,

and so the antithesis is not a true one. As for the Aristotelean

contention that the elements move directly towards and awayfrom the centre of the universe along straight lines, Galileo replies:

1 "The System of the World in Four Dialogues," translated by ThomasSalusbury in his Mathematical Collections (London, 1661), vol. I, p. 20.

no THE SCIENTIFIC REVOLUTION

If another should say that the parts of the Earth, go not in their

motion towards the Centre of the World, but to unite with its Whole ,

and that for that reason they naturally incline towards the centre of

the Terrestrial Globe [a notion distinctly reminiscent of William

Gilbert], by which inclination they conspire to form and preserve it,

what other All, or what other Centre would you find for the World,to which the whole Terrene Globe, being thence removed, wouldseek to return, that so the reason of the Whole might be like to that of

its parts? It may be added, that neither Aristotle nor you can ever

prove, that the Earth de facto is in the centre of the Universe; but if

any Centre may be assigned to the Universe, we shall rather find

the Sun placed in it.

A number of propositions in mechanics are carefully elucidated,

and it is made apparent that the opposition of the Copernican to

the traditional world-picture will depend upon his completelydifferent analysis of the properties of moving things. Mechanics

in fact is the foundation of cosmology:

. . . none of the conditions whereby Aristotle distinguisheth the Coeles-

tial Bodies from Elementary [i.e. terrestrial], hath other foundation

than what he deduceth from the diversity of the natural motion of

those and these; insomuch that it being denied, that the circular

motion is peculiar to Coelestial Bodies, and affirmed, that it is agree-able to all Bodies naturally moveable, it is behooful upon necessary

consequence to say, either that the attributes of generable or in-

generable, alterable or unalterable . . . equally and commonlyagree with all worldly bodies, namely, as well to the Coelestial as to

the Elementary; or that Aristotle hath badly and erroneously de-

duced those from the circular motion, which he hath assigned to

Coelestial Bodies. 1

That is^ if the earth moves, all Aristotle's physical theory of

cosmology,js Baseless? Soon IHteFThis,"* Galileo makes the generaldiscussion of the "architectonics" of the world break down on the

argument that hot and cold are not qualities proper to the heavenlybodies. That sort of dictum (he remarks) leads to

*

a bottomless

ocean, where there is no getting to shore; for this is a Naviga-tion without Compass, Stars, Oars or Rudder.' Accordingly the

debate shifts to the evidence for or against the changelessness of

the heavens, in which the new observations made with the tele-

scope are fully discussed, and a detailed comparison is made

1Salusbury, op. cit. 9 p. 25.

THE ATTACK ON TRADITION: ASTRONOMY in

between the optical properties of the earth and the moon. From this

their physical similarity is deduced. Incidentally Galileo pointsout the futility of the notion that changes in the celestial regionwould be impossible because they would be functionless in the

context of human life, the purpose of the heavenly bodies being

sufficiently served by their light-giving and regular motion. Nordoes he pass over the curious judgement which made sterile im-

mutability a mark of perfection: rather if the earth had continued* an immense Globe of Christal, wherein nothing had ever grown,altered or changed, I should have esteemed it a lump of no greatbenefit to the World, full of idlenesse, and in a word, superfluous.'

By such asides as these, in a strictly scientific argument, the values

of conventional thought were challenged in turn, its texture madeto seem weak and strained.

The second Dialogue opens with caustic mockery of foolish

deference to Aristotle's authority: 'What is this but to make an

Oracle of a Log, and to run to that for answers, to fear that, to

reverence and adore that?' Those who use such methods are not

philosophers but Historians or Doctors of Memory: our disputes,

says Galileo, are about the sensible world, not one of paper. As for

the motion of the earth, it must be altogether imperceptible to its

inhabitants, 'and as it were not at all, so long as we have regard

onely to terrestrial things/ but it must be made known by somecommon appearance of motion in the heavens; and such there is.

1

But in so far as motion is relative, the science of motion cannot

decide whether earth or heaven really moves. 2Consequently

opinion turns on what is "credible and reasonable." It is morereasonable that the earth should revolve than the whole heaven;that the celestial orbs should not have contradictory movements;that the greatest sphere should not rotate in the shortest time; that

the stars should not be compelled to move at different speeds with

the variation of the Poles. On all these points Galileo's view of

what is"re^pnabls." supposes a different perspective from that

of anti-Cbpernican philosophers; but Simplicius is not allowed to

argue the matter, and merely remarks that 'The business is, to

make the Earth move without a thousand inconveniences.' The

1Salusbury, op. cit. t p. 97.

2 *

Motion is so far motion, and as Motion operateth, by how far it hathrelation to things which want Motion: but in those things which all equallypartake thereof it hath nothing to do, and is as if it never were.*

ii2 THE SCIENTIFIC REVOLUTION

first group of"inconveniences" to be dealt with includes the usual

mechanical phenomena, the stone falling vertically, the cannon-

ball ranging equally far east and west, which it was thoughtwould not occur if the earth moved beneath. They naturally lead

Galileo into a long exposition of his new ideas on mechanics, in

which a partial version of the law of inertia is enunciated. Muchof this reasoning against the Aristotelean doctrine of motion had

already been exactly anticipated by the impetus philosophers of

the middle ages. There is a long discussion of the so-called devia-

tion of falling bodies a problem which attracted attention inter-

mittently throughout the seventeenth century as affording a

possible proof of the earth's rotation. It had been alleged, for

example by Tycho Brahe, that if a stone was allowed to fall freely

from the top of the mast of a moving ship, it would not fall at the

foot of the mast, but well aft. Galileo shows that this is inconsistent

with the true principles of mechanics. In spite of Simplicius' cry4 How is this? You have not made an hundred, no not one proof

thereof, and do you so confidently affirm it for true?', Galileo

places his faith in a priori reasoning to predict the result of an ex-

periment he has never made, though previously he has taken painsto point out (against Aristotle) that experiment is always to be

preferred to ratiocination. Therefore, since all heavy bodies have

inertia: 'we onely see the simple motion of descent; since that

other circular one common to the Earth, the Tower and our selves,

remains imperceptible, and as if it never were, and there remaineth

perceptible to us that of the [falling] stone, onely not participatedin by us, and for this, sense demonstrateth that it is by a right line,

ever parallel to the said Tower.' 1

In his attempt to analyse the true path followed by a falling

boHyTrT space the resultant of its double motion about and

towards the centre of the earth^Galileo committed a seripus error

caused by his imperfect definition oTTnertlaT motion. Thoughfamiliar with the common effects of centrifugal force, he over-

looked the fact that the inertial motion of the falling sfone is alonga tangent to the earth's surface, so that in the absence of gravityit would never describe a circle about the earth's centre unless it

was held to it in some way, but would continue along a straightline into space. Galileo thought, on the contrary, that its inertia,

impetus or virtus impressa could cause a free body to revolve in a1Salusbury, op. '/., p. 143.


circle, and so he declared that if a stone fell at a uniform velocitytowards the centre, its compound path would be an Archimedean

spiral. Since the motion of descent is accelerated, however, hedevised a demonstration showing that the true path in space is

probably an arc of circle. Marin Mersenne, who obtained the

accurate law of inertia from Descartes, described this curve cor-

rectly in 1644 as a paraboloid. It is possible that Galileo was in-

4uced to make this error, which he never corrected despite its

incongruity with the parabolic theory of projectiles worked out

in the Discourses^ because of his preconception in favour of perfectcircular motion. Eager to prove that even the local motions of

terrestrial bodies are truly circular, as further testimony against the

Aristotelean antithesis between circular-celestial and rectilinear-

terrestrial displacements, he also noted that, on his theory, the

absolute velocity in space of the falling body is uniform, accelera-

tion relative to the earth's surface being only apparent. This

being so, the question of finding the cause of acceleration, whichhad made Galileo doubtful of the original impetus theory manyyears before, could be shown to be spurious; the problem is

solved by denying absolute acceleration in falling bodies alto-

gether, and visualizing the phenomenon of relative acceleration as

the product of the uniform movement ofobserver and object along

intersecting circular paths.With one exception the mechanical objections that could be

raised against the earth's diurnal revolution are disposed of by

appeal to the principles of inertia and of the relativity of motion

which Galileo illustrates with a variety of ingenious examples.Other problems in mechanics auxiliary to the main argument are

touched upon, such as the conception of static moment, the iso-

chronism of the pendulum, and the ^aw of falling bodies, here

quoted by Galileo without proof/In replying to the objection that

the rotation of the earth would hurl downbuildings, etc., Galileo

makes the first investigation into centrifugal forces^ Using the

idea of virtual forces, enunciated in connection with static

moment, he proves that with equal peripheral velocities the force

is inversely proportional to the radius. He points out that the

angular velocity of the earth is very small, and its radius very

large: therefore the force set up would not be sufficient to over-

come a body's natural gravity. From Galileo's argument ('thus

we may conclude that the earth's revolution would be no more

u4 THE SCIENTIFIC REVOLUTION

able to extrude stones, than any little wheel that goeth so slowly,

as that it maketh but one turn in twenty-four hours') it is clear

that he did not realize that when angular velocities are equal, the

centrifugal force is directly proportional to the radius. It was not

indeed till much later that the rotatory stresses in equatorial regions

were detected.

The: extensive il^ of the perfect agreement between the

heliocentric theory and a rational natural philosophy is certainly

Gajito'jLTOM^ TOIn this there was no conflict of principle between the new philo-

sophy and the old: they were agreed that the science of motion

was the foundation of physics, and that physics and astronomymust speak the same language. Galilean mechanics was thus the

necessary complement to Gopernican astronomy, and though it

is true (as Professor Heisenberg has remarked)1 that nothing could

have been more surprising to the scientists of the seventeenth

century than their discovery that the same mechanical laws were

appropriate for celestial and terrestrial motions alike, on the

smallest and largest scale, the coincidence was not fortuitous, for

it followed from Galileo's conscious endeavour to interpret

Copernicus' mathematical model in terms of natural philosophy.There could be no question as Galileo frequently emphasizes in

the course of the Dialogues of proving that the Copernican

hypothesis was necessarily true; but with the readjustment of

physical ideas effected by him it could be shown to be at least

as plausible as the Ptolemaic. Aristotle's physical theory of the

cosmos, terrestrial and celestial, had been an integral whole; for

Galileo astronomy and physics were so far independent that he

acknowledged the incompetence of purely physical observations

to determine the system of the world, but he had no doubt that

the same laws of motion were universally applicable, to celestial

and terrestrial bodies alike, even to the point of satisfying himself

that if the planets had fallen freely towards the sun from the samedeterminable point, they would have acquired, when they hadattained their actual orbital distances from it, the velocities with

which they actually revolve about it. A true mechanical theory,besides wholly destroying all physical objections to the helio-

centric system, actually created a preponderance of belief in its

favour.

1Philosophic Problems of Nuclear Science (London, 1952), p. 35.


In the Third Dialogue Galileo takes up the arguments for and

against the annual motion of the earth. Beginning with purelyastronomical considerations, he makes plain his distrust of the

quantitative measurements of his own time, from which, however,he confirms that the new star of 1572 was truly celestial. Theirradiation of light, exaggerating the stars' and planets' apparent

diameters, is next explained, and the observations are proved to

verify the Copernican arrangement. Galileo then discusses, in an

eloquent and lucid exposition, the problem posed by the absence

of a detectable stellar parallax. He was not of the opinion that the

stars are infinitely remote, but he does argue that the size of the

universe is such that its dimensions are beyond human standards

of magnitude. If its immensity can be grasped, then it cannot be

beyond the power of God to make it so immense; if its immensityis beyond comprehension, it is none the less presumptuous to

suppose that God could not create what the mind cannot compre-hend. Simplicius objects that a vast region ofempty space between

the orbit of Saturn and the fixed stars would be superfluous and

purposeless, so that Galileo can again condemn the introduction

of teleological reasoning into science. 1 He appears to think that

the remoteness of the fixed stars, though vast, is not to be exag-

gerated, and calculates that even if the radius of the stellar spherebore the same proportion to the semi-diameter of the earth's

orbit, as that bears to the radius of the earth, a star of the sixth

magnitude would still be no larger than the sun, which is,

according to Galileo's reckoning, five and a half times as big as

the earth. The assiduity and skill of astronomers in makingobservations of stellar parallax is in any case doubtful, since these

would demand 'exactnesse very difficult to obtain, as well byreason of the deficiency of Astronomical Instruments, subject to

many alterations, as also through the fault of those that managethem with less diligence than is requisite. . . . Who can in a

Quadrant, or Sextant, that at most shall have its side 3 or 4braccia long, ascertain himself. . . in the direction of the sights, not

to erre two or three minutes?' 2

Galileo's general explanation of the manner in which the

heliocentric theory "saves the phenomena" is modelled on that

ofJ3opernicus, save that he denies the reality of the third motion

1 A teleological argument is, however, used by Galileo himself later.1Salusbury, op. cit., vol. I, p. 351.

n6 THE SCIENTIFIC REVOLUTION

which Copernicus had ascribed to the earth in order to account

for the parallelism of its axis. Thus, for instance, the principle of

the relativity of motion solves the appearance of stations and

retrogressions in the planets. But Galileo nowhere indicates that

their orbits, which Copernicus hadTmaHe eccentric, are other than

docs he attempt to Justifo

particular orbits from the recordsuof positional astronomy. He

further differs from Copernicus in making the centres of the orbit;

coincident with the body of the sun, tt cannot be said, therefore

that Galileo improved the Copernican argument in terms o;

technical astronomy in the Dialogues, except through his use oL

the new qualitative evidence derived from the telescope, which

had already been commented upon in his earlier writings. Indeed,

the extremely simple astronomical model described is flatly

incompatible with precise observation. Galileo, it is clear, was

far more confident of the truth of the mechanical principle that

bodies possess the property of inertial rotation in a perfect circle

than of the accuracy of astronomical measurements. It was a

characteristic of his scientific method of abstraction that it could

more easily analyse, and describe in mathematico-mechanical

language, a version or model of the real phenomena which was

less complex than the phenomena themselves; and Galileo was

not always sufficiently conscious of the genuine significance of the

greater complexity. In this instance Galileo was deceived, partly

by his imperfect definition of inertia (only implicitly rectified in

his discussion of centrifugal force) and partly by lingering astro-

nomical ideas. It is noteworthy that, while he does not consider

whether the spheres are real or not, the word itselfhe uses naturally

and without comment. A perfectly balanced, hollow sphere, or a

circle, could of course be properly imagined to rotate inertially as

a rigid body carrying round with it a planet. It seems, therefore,

that Galileo, whose approach to the problem was kinematic

rather than truly dynamic, did not sufficiently reflect upon the

consequences of taking away the heavenly spheres, and leaving

the stars and planets as free bodies in space if indeed this was

firmly his conviction. Unlike Newton, Galileo never comparedthe motion of a planet to that of a projectile; unlike Kepler, he

did not know that the geometry of planetary orbits vitiated anykind of spherical model.

The scientific work of Johann Kepler (1571-1630) was of an


utterly different quality from that of Galileo. The Dialogues, and

to a less extent the Discourses ,are popular books. In them Galileo

does not fear to explain many elementary matters with which the

expert would already be well acquainted. Kepler's writings, on

the other hand, are so highly abstruse that the spread of his ideas

was retarded by the difficulty of discovering and understanding

tlierrirThey required that the reader be fully trained in the

elaborate mathematics of positional astronomy. As Galileo was

complementary to Copernicus, so the mathematician Kepler was

complementary to Galileo, and there is perhaps no more remark-

able example of the way in which two cognate, yet unlike, minds

can follow parallel paths without interaction. Both Galileo and

Kepler sought to strengthen the Copernican doctrine; they

corresponded, and referred favourably to each other; but there

is no shred of evidence that either was to the slightest degree

deflected from his own course, or impelled to modify his own

ideas, by the other's work. The synthesis of their two distinct points

of view was only effected a generation later; until then Keplerand Galileo had as little in common as Ptolemy and Aristotle. As

in the traditional, so also in the new science of the early seven-

teenth century this failure to overlap was not due to fortuitous

causes, nor to any lack of sympathy between the two modes of

approach. It was simply that the key by which a synthesis could

be effected was not yet found. A cosmological dichotomy existed

in Hellenistic science because physics and positional astronomy

required similar, but not identical models; a comparable dicho-

tomy existed from about 1630 to 1687 because there was no wayin which the observed celestial motions could be interpreted in

accordance with the kinematical principles of Galileo. The two

lines of progress could only be brought together by a higher

generalization for which dynamics was essential and kinematics

inadequate.

Kepler was the discoverer of the new descriptive laws of plane-

tary motion^ but he"achieved more than this, for he made the

nTst .suggestion^ towards a physical theory of the universe adapted

to the necessities of the new description. Although his life was

given over to mathematical drudgery in which he was aided bythe much improved trigonometry of his day, and the invention of

logarithms Kepler was a man of vigorous and original scientific

imagination.- The mathematical operations he set himself could

ii8 THE SCIENTIFIC REVOLUTION

hardly have proved creative without it. In his first work he soughtfor the divine canon in celestial architecture, and this pursuit

ran through all his later computations. But Kepler was no emptytheorist: the divine art of proportion, the harmony of the grand

design of nature, was to be elucidated from the most precise

mathematical observation of the universe. Hence the turning-

point in his career, the necessary foundation for his work, was

Kepler's cncpûjr^r_with theJDaiiish astronomer, Tycho Brahc

(1546-1601), who, after a quarreTwiBT King Christian IV, had

deserted his royally endowed observatory at Hveen to enter the

service of the eccentric Emperor Rudolph II, patron of alchemists

and astrologers, at Prague. Thither Kepler was drawn from Graz

in Styria by the undigested mass of observations, of unparalleled

accuracyTwhich Tycho hadnSi^gTirwiffi^Tirni. UHimalelyHtneafletiiiiulatEd- result of thirty years' labour yielded up the three

laws ofplanetary motion which, as Kepler framed them, contained

the decisive argument against the geostatic hypothesis so warmlydefended by Tycho.

^sn astronomer'sjrole in the early history

ojjrnodern astrpjiomyîs ânalogousJoijhatJ)f

Perhaps he was even more fully than the anatomist the first

modern exponent of the art of disinterested observation and

description. For if Tycho imported into his astronomical theorydominant factors which were physical in nature, it cannot be

said (as it may of Vesalius' physiological preconceptions) that the

evidence to confute them lay before his eyes. The problem of

attaining precision was no less real for him than for Vesalius, and

the methods he devised to solve it were probably more original.

And certainly Tycho was unique among early modern scientists

in his insistence upon the crucial importance of accurate quanti-tative measurement; always a desideratum in astronomy, cer-

tainly, but never previously handled with the analytical andinventive powers of Tycho, who first consciously studied methods

of estimating and correcting errors of observation in order to

determine their limits of accuracy. The most accurate predecessorsof Tycho were not Europeans, but the astronomers who workedin the observatory founded at Samarkand by Ulugh Beigh, about

1420. Their results were correct to about ten minutes of arc

(i.e. roughly twice as good as Hipparchus'); Tycho's observations

were about twice as good again, falling systematically within


about four minutes of modern values. 1 This result was achieved

by patient attention to detail. The instruments at Hveen were

fixed, of different types for the various kinds of angular measure-

ment, and much larger than those commonly used in the past,

so that their scales could be more finely divided. They were the

work of the most skilful German craftsmen, whom Tycho en-

couraged by his patronage and direction. He devised a new form

of sight, and a sort of diagonal scale for reading fractions of a

degree. In measuring either the longitude of a star, or its right

ascension, it is most convenient to proceed by a way that requiresan instrument measuring time accurately, and Tycho studied the

improvement of clocks for this purpose: but he found that a new

technique of his own by which observations were referred to the

position of the sun was more trustworthy. He was the first

astronomer in Europe to use the modern celestial coordinates,

reckoning star-positions with reference to the celestial equator,not (as formerly) to the ecliptic. 4n^tkQ,,klaYa.UQa in, his

pracUcc^was the observation of planetary positions not at a few

isolated points in the orbit (especially when in opposition to the

sun), but at frequent intervals so that the whole orbit could be

plotted.

The techniques and standards of precision in astronomy, of

which Tycho was the real founder, were evolved slowly over a

period of thirty years to fulfil a very simple ambition. When he

made his first observations with a home-made quadrant, he found

that the places given in star-catalogues were false, and that events

such as eclipses occurred as much as two or three days from the

predicted times. As the Copernican "Prutenic Tables" were

computed from old observations they had brought in no significant

improvement. The task Tycho set himself, therefore, was very

simple: to plot afresh the positions of the brightest stars, and with

the fundamental map of the sky established to observe the motions

of sun, moon and planets so that the elements of their orbits could

be recalculated without mistake. It does not seem that he under-

took this with any violently partisan intent, but it is likely that he

wished to show the falsity of the Copernicans' claim to have

1 As was first pointed out by Robert Hookc, the unaided human eye is

incapable of resolving points whose angular separation is less than about twominutes of arc, so that Tycho's work approximately attains the minimumtheoretical limits of accuracy for instruments such as he used.


increased the accuracy of celestial mathematics, and to bolster

up the geostatic doctrine by publishing unimpugnable tables and

ephemerides calculated upon that assumption. To vindicate the

"Tychonic" geostatic system was the last ambition of his life,

which he charged Kepler to fulfil. However, he was no slavish

adherent to conventional ideas. He did not believe that apparent

changes in the sky were due to meteors in the earth's atmosphere;he proved that comets were celestial bodies, and that the spherescould have no real existence as physical bodies since comets pass

through them; and his description of the planetary motions

is relativistically identical with that of Copernicus.1 As an

astronomer, indeed, Tycho in no way belonged to the past: it

was as a good Aristotelean natural-philosopher that he believed

the earth incapable of movement.

Tycho's observations, including his catalogue of 1,000 star-

places, have not proved of enduring value. The earliest observa-

tions that have an other than historical interest are those of the

English astronomer, Flamsteed, early in the eighteenth century

(error c. ten seconds of arc), for within about sixty years of Tycho'sdeath the optically-unaided measuring instrument, still ardentlydefended by Hevelius of Dantzig, was beginning to pass out of

use. Within a century Tycho's tables had been thoroughly revised

by such astronomers as Halley, the Cassinis, Roemer and Flam-

steed. In the interval, however, Kepler's discoveries based on

Tycho's work had become recognized. To appreciate the relation-

ship between Kepler and Tycho the inventive mathematician

and the patient observer it must be realized that the balance of

choice between Keplerian and Copernican astronomy is verynarrow. Until measurements were available whose accuracycould be relied upon within a range of four minutes, or even less,,

there was no need to suppose that the planetary orbits were any-

thing other than circles eccentric to the sun. Kepler, in plottingthe orbit of Mars, from which he discovered the ellipticity of

planetary orbits in general, was able to calculate the elements of

a circular orbit which differed by less than ten minutes from the

observations. It was only because he knew that Tycho's work was

accurate within about half this range that he was dissatisfied and

1 The point about comets was not noticed by Galileo, some of whose other

arguments cannot be directed against the "Tychonic" version of the geostaticidea.


impelled to go further. Kepler's famous ^^First La\^was thus the

first instance in the history oscience of a discovery bein&made as

the result of a search for a theory, not merely to cover a given set

of observations,Jyt tgJntcrPrct a

"

grQUP Cr?^2:e

^ measurements

whose probaEIe^ accuTacy^vas la significant factor, discrimination

between measurement in a somewhat casual sense, and scientific

measurement, in which the quantitative result is itself criticized

and its range of error determined, only developed slowly in other

sciences during the course of the scientific revolution.

While Kepler's discoveries would have been impossible without

the refinement of observation attained by Tycho Brahe, more than

mathematical precision was involved in them. Before the tele-

scope, the only materials available for the construction of a

planetary theory were angular measurements principally deter-

minations of the positions of the planets in the zodiac when sun,

earth and planet were in the same straight line. Consequently the

most that a planetary theory could achieve was to predict the

times at which a planet would return to the same relative situa-

tion, and its position at those times. The mathematical analysis of

the solar system as a number of bodies moving in three-dimensional

space had never been attempted, as such, by the older astronomers,who had been content to assign such problems to philosophers.

They had never concerned themselves with the real path of a

planet in space, so long as their model predicted with tolerable

accuracy the few recurrent situations in which observations could

easily be made. The whole tendency of the scientific revolution was

to rebel against this view of the astronomer as a mathematician, a

deviser of models to save the phenomena, and to see astronomyas a science comprehending the totality of knowledge concerning

Jtjie heavens and the relations of the earth to the celestial regions.

Copernicus had abolished the equant because it was a mathe-

matical fiction, an unphilosophical expedient. Galileo modified

Copernicus' universe even further in the direction of physical

explicability. Kepler had a true conception of the universe as a

system of bodies whose arrangement and motions should reveal

common principles of design or in more modern language, be

capable of yielding universal generalizations which were to

be demonstrated from the observations, not from physical or

metaphysical axiomSjTor Kepler the astronomer's task was not

to study the universe piecemeal to construct models for each


separate planet but by studying and interpreting it as a whole

to prove that the phenomena of each part were consistent with

a single design. His aim was to provide a fitting philosophical

pattern for the new discoveries of mathematical astronomy: 'so

that I might ascribe the motion of the Sun to the earth itself by

physical, or rather metaphysical reasoning, as Copernicus did bymathematical,' he remarked in the preface to the Cosmographic

Mystery. Exact science might properly make inroads upon the

established prerogative of philosophy; it was far from being his

purpose to expel natural-philosophical considerations from quan-titative science altogether.

Indeed, Kepler's scientific work was critically influenced by his

attachment to extra-scientific ideas. He had firm preconceptions,and he was strongly opposed to mere phenomenalism. Even morethan Copernicus he was infected with Pythagorean mysticism,and fascinated by the primary, foundational significance of purelynumerical relations. He could elaborately interpret his descriptive

in ajs^ terms of musical harmony

genuine"music of the spheres"; draw the analogy between sun,

fixed stars and planets, and God the Father, the Son and the Holy

Qhost; or discuss the aspects of the planets at the moment whentnfe"Cosmos was created. Some of the questions which he sought to

answer are, to later minds, absurd or meaningless. Rightly he held

that the question, why are the appearances thus and not other-

wise, requires a scientific (rather than a purely philosophic)

answer, and he was the first astronomer to take a serious grasp of

it, but for him also such a question as, why are there no more and

no less than five planets, was also urgent. As Kepler handled it,

the inquiry involved an unshaken medieval complacency in the

certitude of knowledge. His first explanation was given in the

Cosmographic Mystery (1597), where he adopted the theory that

the design of the universe is modelled upon the series of five

geometrically rcgiJarn^ to find a

rationale for the'dimSnsiolis^TlTie "planetary orbits as calculated

by Copernicus by considering them as mathematical series, or as

circles described round regular polygons. The number five was

certainly accounted for in this theory, and moreover Keplerfound that if the regular solids were supposed to be fitted each

inside a sphere, and these within each other in a certain order, the

dimensions of the six spheres so arranged corresponded approxi-


mately to those of the earth and five planets. In the Cosmographic

Mystery Kepler argued trenchantly in favour of the Copernican

system, which he modified in order to make the sun its central

point, instead of the centre of the earth's orbit. Believing that the

imperfect agreement between his theory and Copernicus' determi-

nations might be due to faulty observation, he had good hope of

confirming it with the aid of the more accurate measurements

of Tycho Brahe.

As Tycho's assistant at Prague, Kepler was directed to perfectthe theory calculated in accordance with the observations onMars by Tycho's Danish assistant, Longomontanus. The result

was published in the New Astronomy or Celestial Physics, a book sub-

sidized by the Emperor Rudolph II and published in 1609, eight

years after Tycho's death had released Kepler from adherence to

Tycho's geostatic system. His first discovery was that the plane of

the orbit of Mars passed through the sun (a point in favour of

Copernicus) and was invariably inclined to the ecliptic. A major

problem was the planet's unequal velocity in its course. Although

Kepler restored the equant-point, and so could adjust the varying

angular velocity of Mars with respect to the sun in different pro-

portions, he found that no single position of the equant-pointwould give a rate of variation satisfying all the observations. Thesame difficulty occurred when the earth's orbit was considered.

Kepler found that its motion was certainly faster when near to the

sun than when most remote from it, but not in such a way that the

angular velocity about any arbitrary fixed point within the circle

was uniform. 1 The problem one after Kepler's own heart was

to find a theorem denoting this variation in velocity, an equation

relaiing the speed of the planet's rotation at any point to its

distance from the sun. Here Kepler was assisted by a quasi-

philosophical notion that it was a "moving spirit" in the sun

itself which caused the planet's circumgyrations. '1 he further the

planet receded from this spirit, the more weakly its force would

operate, and so the planet's velocity would lessen. This anima

matrix is referred to in the Cosmographic Mystery as hurrying alongthe stars (i.e. planets) and comets which it reaches, with a swift-

ness appropriate to the distance of the place from the sun, and the

1 This was the first mathematical proof that the motion of the earth (or,

as Ptolemy would have said, of the sun) is strictly identical with that of the

planets.


strength of its virtue there.1 The problem Kepler set himself, of

assigning a determinate motion to a body revolving round a fixed

point in an eccentric circle so that it moves through equal in-

finitesimal small arcs in times proportional to its distance from

the point, is one that can be solved by integration. He used a

method similar to that by which Archimedes had long before

evaluated TT, and so arrived at his "second" planetary law, that

the, radios-vector between sun and planet sweeps over equal areas

of the orbit in equal times. Though his first proof was open to

criticlsmTKepler was later able to satisfy himself that the various

errors in his method cancelled each other, so that the law was

rigorously true. 2

At this stage in his complex and tedious calculations involvingthe geometrical analysis of many theoretical possibilities, as well

as the continual checking of the predicted motions against ob-

servations selected from Tycho Brahe's great store Kepler was

already convinced that the orbit of the earth or a planet could

not be a perfect circle eccentric to the sun. As he said:

The reflective and intelligent reader will see, that this opinion amongastronomers concerning the perfect eccentric circle of the orbit in-

volves a great deal that is incredible in physical speculation. . . . Myfirst error was to take the planet's path as a perfect circle, and this

mistake robbed me of the more time, as it was taught on the auth-

ority of all philosophers, and consistent in itself With Metaphysics.

In calculations of the earth's angular velocity he could assume the

orbit to be circular, because its ellipticity is small (nam insensiie

est . . . quantum ei ovalis forma detrahif), but in the orbits of the

other planets the difference would become very sensible. 8 His next

problem, obviously, was to define the nature of this non-circular

orbit more closely. He therefore returned to the investigations on

Mars, in a far more secure position now that he had worked out

the movement of the observer's platform the earth with greater

accuracy than before. Experiment showed that the orbit of Marscould not, indeed, be circular, for this when compared with the

observations made the motion of the planet too rapid at aphelion

1Kepler: Gesammelte Werke, vol. I, p. 77.

2Ibid., vol. Ill, pp. 263-70.

3 The eccentricity of the earth's orbit is only 0-017, that of Mars is about

5 times as great, and of Mercury 12 times. The error which constituted

Kepler's problem increases roughly as the square of the excentricity.


and perihelion, and too slow at the mean distances. After manytrials Kepler wrote: 'Thus it is clear, the orbit of the planet is not

a circle, but passes within the circle at the sides, and increases its

amplitude again to that of the circle at perigee. The shape of a

path of this kind is called an oval.' Again, the development of

Kepler's thoughts was influenced by his idea of the physicalmechanism which could produce such a departure from the per-

fectly circular form. He supposed that the oval path was traced

by the resultant of two distinct motions; the first being that due to

the action of the sun's virtue, varying with the distance of the

planet, and the second a uniform rotation of the planet in an

imaginary epicycle produced by its own virtus motrix. The hypo-thetical orbit would be an oval (or rather an ovoid, since its apseswould be asymmetrical) enclosed within the normal eccentric at

all points save the apses. Kepler spent much labour in vain at-

tempts to geometrize this hypothesis so that it could be comparedwith observation. Direct and indirect methods were tried, but

Kepler finally had to confess that the oval orbit and the theory of

its physical causation had "gone up in smoke." It was the acci-

dental observation of a numerical congruity that led him to

substitute for the oval an ellipse, which he found could be madeto fit the area-law exactly. Even at this stage he was much dis-

turbed because he could not give a physical meaning to the

elliptical orbit, until he satisfied himself that such an ellipse as he

required would be traced out by a planet supposed to librate on

the diameter of an epicycle.

The third of Kepler's great descriptive theorems, that the

squares of the periodic timesôQhejg^âs tne cubes of tfieir respcctiyje^mâji^which solved the problem upon which hejiad originally embarked,was announced in The Jfarmontes of the World (1619). This strange

book, resuming the theme of the Cosmographic Mystery, has the

same concern with esoteric relationships. Kepler compared the

instantaneous velocities of the planets at different points in their

orbits, and expressed these ratios in terms of musical harmony.He further compared the velocities of the several planets at their

nearest approach to the sun; and finally he was induced to com-

pare, not merely the periods, times and distances of the planets,which he had already discovered to be without significance, but

the powers of these numbers, and so hit upon the "third law." A

I 26 THE SCIENTIFIC REVOLUTION

century and a half later, in 1772, a purely empirical formula

connecting the distances of the planets was used by Johann Elert

Bode to predict the existence of an unknown planet beyondSaturn. His audacity was vindicated by the discovery of Uranus.

The simplicity and directness which these relations introduced

into astronomy need no emphasis. The shapes and dimensions of

the planetary orbits, and the velocities of the planet's motions

within them, could now be calculated with ease and certitude.

Kepler's Laws were the observational axioms upon which

Newtonian celestial mechanics was to rest secure. What is not

obvious is that Kepler's discoveries were displayed in extremelydifficult books, published far from the main foci of scientific

activity in France and Italy, and so were passed over by a genera-tion that ignored their true importance. Kepler himself regrettedthe abstruseness of his subject:

Most hard today is the condition of those who write mathematical

works, especially astronomical treatises. For unless you make use of

genuine subtlety in the propositions, instructions, demonstrations and

conclusions, the book will not be mathematical; if you do use it,

however, reading it will be made very disagreeable, particularly in

the Latin language, which lacks articles and the grace of Greek. Andalso today there are extremely few qualified readers, the rest com-

monly reject [such books]. How many mathematicians are there,

who would toil through the Conies of Apollonius of Perga? Yet that

material is of a kind that is far more easily expressed in figures and

lines, than is Astronomy.1

In truth Kepler was the last of the medieval planetary theorists,

the last laborious computer and porer over tables. Such methods

were too tedious for his own generation, excited by discovery and

the new philosophy, and to a careless reader Kepler's discoveries

were hidden in the idiosyncrasy of his strange speculation. Whenthey were appreciated, new mathematics and new techniques were

framing a new astronomy.But Kepler was more than a mathematician. Perhaps the

importance of his work, apart from the three famous Laws, has

not been sufficiently esteemed. The older historians passed politely

over Kepler's theorizing on physical mechanisms, his love of

analogy, and all that was ancillary to the main mathematical

1 "Astronomia Nova," Ges. Werke, vol. Ill, p. 18.


argument, as so much dross that was best left buried. Now it is

not difficult to see that Kepler was as original and stimulatingin his sidetracks as when following the plain mathematical road.

Certainly his ideas on gravity, on the action of forces at distance,

are important factors in theTprehistory of the theory of universal

gravitation. The Cartesians ridiculed Kepler's mysterious forces

seated in the sun, and his appetites of matter, just as they later

resisted the notion of gravitational attraction. Kepler does makeodd equivalencies between "soul" or "spirit" and force, never-

theless his cosmological theory was mechanistically designed and

designed to give a far more accurate model than those of either

Galileo or Descartes. It was Kepler who, in the Cosmographic

Mystery, denounced the traditional belief in material sphereswhich had been left unchallenged by Copernicus, and on which

Galileo had remained silent:

Neither indeed is to be feared that the lunar orbs may be forced out

of position, compressed by the close proportions of [other celestial]

bodies, if they are not included and buried in that orb itself. For it is

absurd and monstrous to set these bodies in the sky, endowed with

certain properties of matter, which do not resist the passage of anyother solid body. Certainly many will not fear to doubt that there are

in general any of these Adamantine orbs in the sky, that the stars are

transported through space and the aetherial air, free from these

fetters of the orbs, by a certain divine virtue regulating their courses

by the understanding of geometrical proportions.

He went on to ask, by what chains and harness is the movingearth fastened to its orb? and to point out that nowhere on the

surface of the globe do men find it embedded in a material

medium, but always surrounded by air. Kepler, too, must be

credited, at least as much as Descartes, with the perception that

there must be some source of force, or tension, within the solar

system. It could not be a complex of entirely independent bodies

without mutual interaction. It could not be accidental that the

planes of all the orbits passed through the sun, nor could the

variations of the planet's motion the differences in its velocityat perihelion and aphelion, for example be explained^ without

the supposition that some force was acting upon it.jJFpr Galileo

the universe was simple and dynamically constant: in Kepler'sfar more realistic picture it was highly complex and its dynamicalcondition constantly changing. ]Thus it was the Keplerian picture

i 28 THE SCIENTIFIC REVOLUTION

that enforced the development of celestial mechanics during the

late seventeenth century. The descriptive and purely empiricallaws of planetary motion presented a problem that natural

philosophy could not escape. Kepler had gone far beyond the

bounds of the astronomical problem of two generations does the

earth move or not? to assert principles of celestial motion, set in

a pattern of theorizing upon cosmic physics, which displacedtraditional doctrines even more thoroughly.

CHAPTER V

EXPERIMENT IN BIOLOGY

\"\7"THILE ^e ear^V stages f the scientific revolution in its

\\ /physical aspects were strongly positive, the first phaseVV in biology seems by contrast indecisive and inconclusive.

The sixteenth century witnessed the promulgation of new ideals

and new methods of study in such fields as botany and zoology,or anatomy and physiology, but there was as yet no more than the

vague promise of the alternative body of knowledge which the

pursuit of the new ideals and the practice of the new methodswould construct iri due course. Though existing doctrines mightbe criticized, no others had yet taken shape to displace them.

There were criticisms occasionally of exaggeratedly animistic

patterns of explanation; but the application of mechanistic

philosophy to biological problems was not attempted before

Descartes. As the mind abhors a vacuum, the natural result wasa lag of theory behind observation. The authority of Galenendured longer than that of Aristotle because it was intrinsicallyfar more difficult to apply the principles of physics and chemistryto the investigation of physiological processes than to applyGalilean mechanics to astronomy; astronomers also had the

advantage over physicians that mechanics was the first science to

enter a modern stage. The effect of the greater subtlety of the

questions handled by the biologist was, so to speak, to distinguishobservation from conceptualization as separate branches of

scientific activity. Many experiments had been carried out in

physical science to confirm or disprove directly the Aristotelean

pronouncements, when as yet the theory of humours or the

Galenic account of digestion were still untested. Experimentationwas not deterred by technical difficulties alone, for imaginationwas lacking and the whole framework of ideas which would have

given meaning to such experiments had still to be created. Thosethat were planned and successfully carried out such as the well-

known investigation of Sanctorius (1561-1636) into the quanti-tative gain in weight of the body by ingestion and loss through

129


excretion though they produced interesting information, carried

little or no weight for or against the main strategic ideas of

medicine and biology.In a somewhat similar manner, the advance of the encyclopaedic

naturalists of the sixteenth century towards a modern scientific

method was highly specialized and limited in character. Thenaturalist's ideas concerning the origin of organic life, the distri-

bution of plants and animals, and the reasons for their wide rangeof structure and form, were still for the most part non-scientific in

origin, or at best derived from very ancient sources. On the other

hand, he was progressing towards modern ways of classifying and

describing organisms and of defining the subject-matter of natural

history. He became less interested in nature-study as an exercise

in morality; he made a partial distinction between the Flora andthe Pharmacopeia. This brought the disadvantage, however, that

as botanists and zoologists became progressively more efficient in

classification and description, they came near to losing interest in

all other problems posed by the organic world. The naturalist was

limited, in the main, to a particular kind of activity ultimatelyinherited from the apothecaries' need to distinguish medicinal

herbs partly, of course, because it was one task worth doingwhich was within his competence, but partly also because he

lacked the imagination which would have freed him from the

influence of tradition. A different kind of biology, or such crucial

experiments as those of Redi in the seventeenth century on spon-taneous generation and those of Mendel in the nineteenth on

inheritance, was not technically impossible; it did not necessarily

depend altogether upon laboratories, instruments and the dis-

coveries of other sciences. It did require which is a great deal

intellectual originality. It did require the ability to frame questionsabout the living state and ways of proceeding to answer such

questions. This was very different from the compilation of greaterand greater masses of the same type of information.

The vast range of biological and medical science which widenedout during the nineteenth century was, therefore, represented in

the sixteenth only by medicine and natural history: and even

these studies consisted of little more than the endeavour to cure

disease and herbalism, these being in turn closely linked. Thevarious branches of medicine, such as physiology (the functionof organs in contrast to the arrangement of organs, anatomy),

EXPERIMENT IN BIOLOGY 131

pathology, or hygiene were hardly distinguished save as subjects of

separate treatises by Galen. All parts of medical science, excluding

surgery, fell under the general surveillance of the physician. Orhe might become herbalist or zoologist the former in pursuit of

the medical virtues of plants, and the latter as a comparativeanatomist. Therefore it is not surprising that physicians had a

major creative role in the biology of the sixteenth and seventeenth

centuries, nor that the course of the science was to some extent

directed by medical interests. Among the botanists many were

medical men to name only Fuchs, Cordus, Cesalpino, Bauhin,

Tournefort, and Linnaeus himself. Brunfels, whom Linnaeus

called the father of botany, and John Ray, Linnaeus' greatest

predecessor, were exceptions. All the work in human and com-

parative anatomy, and much microscopy (the famous exception

being Leeuwenhoek), was carried out by physicians. Surgeons,

being on a lower academic, social and intellectual level, to which

they were firmly suppressed by the energetic corporate interest

of the physicians, had far less opportunity to add to knowledge.The organization of the scientific movement and the system of

the universities protracted the dual relationship of medicine #nd

biology long after it had ceased to be real when books were

already being written purely on botany, or /oology, or physiology.Nowhere was it possible to obtain formal instruction in any of

these subjects, save as part of a general course in medicine, until

the middle of the eighteenth century. Teachers of botany (or of

chemistry) were appointed only to fulfil the needs of the medical

faculty.

To the young physician of the later sixteenth or seventeenth

centuries, ardent for research, many courses were open. He mightventure on original methods in practice, collect case-histories,

perhaps contribute to the growing literature of abnormal observa-

tions and remarkable cures. Or he might, in the humanistic vein,

seek to improve the general understanding of the magisterialtexts. Or he might practise anatomy, in which case he would

certainly dissect many animals. Or he might embark upon de-

scriptive natural history. But the texture of the scientific work

involved in all these courses was far from identical. The humanist-

physician was easily assimilated to the type of the scholar, the

naturalist-physician to the type of the lexicographer admittedlywith the development ofspecialized powers of observation. Neither


of these courses, at this time, led naturally to the act of experi-

menting. The problem, however, which comes nearest to the

physician's work, the understanding of the functioning of the

human (and, by analogy, the animal) body in health and disease,

is one that lends itself to observation and experiment. The physi-cian must observe and classify diseases, he must also experimentin his therapy. Admittedly the physician found his normal ratio-

cinative background in Galen's ideas, admittedly he proceeded in

accordance with the accepted theory of the nature of disease and

of the measures requisite to effect a remedy; even the ascription

of symptoms to the humoral condition, the amount and timing of

blood-letting and the preparation of drugs were laid down byrules for his guidance more dogmatically than they are today.

Yet, whatever the teaching, in any age a physician must be some-

thing of an empiric. He must learn to use his own judgement. Hemust adapt general principles to particular cases. And in the

sixteenth century the art of medicine was far from static. Apartfrom the great variety of herbal medicaments among which the

physician had to make his choice, there were the new inorganic

remedies, such as mercury, and new drugs from the East and WestIndies. There was a great controversy over the correct procedurein venesection. There were new problems syphilis, gunshot

wounds, scurvy ravaging crews on long ocean voyages, and plagues

flourishing with the growth of cities. A physician's practice could

be guided by principles the use of contraries to restore the balance

of the humours, or analogy (dead man's skull, powdered, in cases

of epilepsy) but he could be no mere follower of the book, if

only because the book was an inconsistent and insufficiently

specific guide. The most important part of medicine was learnt

through experience, and profitable experience depends on

experiment.

Perhaps this lesson was the most enduring contribution madeby Paracelsus to true science. Naturally when Paracelsus writes,

for example,' From his own head a man cannot learn the theory

of medicine, but only from that which his eyes see and his fingerstouch . . . theory and practice should together form one, andshould remain undivided. . . . Practice should not be based on

speculative theory/ it has to be remembered that "practice" for

Paracelsus meant something very different from the rationalist

practice of the modern physician. He accepted the doctrine of


signatures; he taught the doctrine of the microcosm and the

macrocosm that forced the physician to become astrologer; to

him medicine was the study of the occult forces that play uponthe human body. Within his conception of the physician's practice

however, he was empirical. The teachings of Aristotle and Galen

provoked his unmitigated scorn, and he castigated the academic

physicians who relied upon the theories derived from them. Heclaimed himself to have learned the art of healing not only from

learned men, but from wise women, bathkeepers, barbers and

magicians. Ideally, for him, the test of a remedy was its efficacy,

though in his devotion to the occult and the esoteric he often fell far

short of this ideal. Believing that experience was the best teacher, he

did not hesitate to experiment with medicaments of which the aca-

demically minded were fearful, and so he became the leader of

the chemical school in therapy. The strongest poisons, he held (nodoubt arguing from the virtues of mercury or opium) , contained

hidden arcana, serviceable to the physician initiated into their

mysteries. No doubt the latitude which Paracelsus introduced into

medical practice was usually profitless and frequently dangerous;but it stimulated a more rationalist empiricism than his own. Notfor the first time, the experimentalism of magic was favourable to

the growth of natural science.

Of course trial-and-error methods do not constitute a new

philosophy of science. Ambroise Park's use of ligatures and dress-

ings instead of cauterization by fire is not to be put forward as an

example of a conscious experimental science though it was a

genuine revolt against authority, and a genuine instance of em-

piricism. Pare knew no Latin: he was only the royal surgeon. Butit is to a certain degree inevitable that the originally minded menwho adhered to the more practical aspects of medicine, who were

compelled to be empirical (Glauber, after all, must have tested

his sal mirabile), should have moved more naturally in the direction

of experiment than their colleagues whose interests ran otherwise.

From dissection for research to experiment of a limited kind is not

a great step. Anatomical observations on the veins and arteries

suggested simple experiments on the behaviour of the blood in the

living body with which venesection made the surgeon necessarily

familiar. Observations involving vivisection had been made longbefore by Galen and Aristotle, and were repeated in the sixteenth

century: wounds occasionally gave opportunities for a glimpse


beneath the surface. There was almost a tradition by which

poisons and their antidotes were tested upon small animals (andsometimes condemned criminals). Moreover, the Hellenistic tradi-

tion in zoology and physiology offered perhaps the best model of

experimental science that could be found in the whole corpusof transmitted learning. The Aristotle of the Generation of Animals

and the History of Animals was an experimenter as well as an ex-

cellent observer. In embryology especially again leaving aside

all question of theory the sixteenth-century heritage of experi-

ment is clear. Albert the Great, like Aristotle long before, had

opened eggs systematically. The men of the renaissance had onlyto continue a well-defined course of investigation.

Perhaps it is not stretching imagination to see practical medi-

cine playing somewhat the same role in the development ofbiologyas that of technology in the evolution of the physical sciences. The

physician, engineer and manufacturer had that practical skill in

their encounters with nature which was lacking to the reflective,

generalizing philosopher of the study. They wove a strand of

empiricism into the web of theory. They were equally (if honest

and intelligent men) more interested in the attainment of tangibleresults than the discussion of means by which such results oughtto be attainable. And just as experience with cannon or in indus-

trial chemistry had no simultaneous, directly positive effect uponideas of motion or the four-element theory of matter, so also

empiricism in medical science could not immediately and pro-

portionately modify the broad theory of physiology or pathology.The impact of empiricism was in all cases gradual, subject to

variations in emphasis and liable to be different from that which

posterity might deduce merely by treating practical experienceas the

"cause," and change in theory as the "effect."

The history of the discovery of the circulation of the blood is

an illuminating instance of the delayed action of observation and

experiment upon biological theory. Harvey had little that wasnew in the way of fact available to him. His great merit was to

integrate known but ineffective facts into a new and comprehen-sive generalization. As he himself constantly reiterates in his

treatise On the Motion of the Heart (1628) for he was one of those

innovators who had little desire to flout authority unnecessarily

many of the observations on which he relied were already knownto Galen. Harvey indeed did not so much contradict Galen as


gently convert his doctrines. Other observations must have beenmade at almost every venesection if only physicians less intelli-

gent than Harvey had been able to see their meaning. Thoughtheir function was imperfectly understood, the valves in the veins

had been observed more than sixty years before Harvey's dis-

covery of the circulation was made; the tricuspid and mitral

valves in the heart, which were also given a rational function for

the first time by Harvey, had been described by Galen Himself. In

many ways, therefore, Harvey's discovery in biology resembled

Galileo's in mechanics in being a new interpretation of familiar

data drawn from common experience, and Harvey, like Galileo,

had numerous precursors.

Harvey, however, made a far more precise appeal to experi-mental evidence than did Galileo, and his use of a

"critical in-

stance" (though there seems to be nothing to suggest that Harveywas at all influenced by his great patient, Francis Bacon) is not

paralleled in mechanics. The greatest physiologist of the sixteenth

century, Jean Fernel, had not known how to apply the experi-mental method. Sir Charles Sherrington has expressly pointed the

contrast between him and Harvey:

Fernel, it would seem, in order to do his work, must find it part of a

logically conceived world. His data must be presented to him in a

form which, according to his own a priori reasoning, hangs together.In that demand of his lies his inveterate distrust of empiricism. "Wecannot be said to know a thing of which we do not know the cause."

And under "cause" he included not only the "how" but the "why."With Harvey it was not so. When asked "why" the blood circulated,

his reply had been that he could not say. Fernel welcomed "facts,"

but especially as pegs for theory; Harvey, whether they were such

facts or not, if they were perfectly attested. 1

To Harvey, anatomy offered the elementary facts of physio-

logy; Fernel, however, wrote that 'in passing from anatomy to

physiology that is to the actions of the body we pass from

what we can see and feel to what is known only by meditation.'

He had liberated himself from the occult influence of the stars,

but a mechanistic interpretation of physiological process was still

alien to his thought. For him the origins of bodily actions hadto be sought in the soul, the non-material entity controlling and

1 The Endeavour ofJean Fernel (Cambridge, 1946), p. 143.


directing the operations of the material parts. In this, of course,

he simply followed Galen and the Greek tradition.

The ancients had studied the three most obvious instances of

the involuntary physiological process respiration, the beating of

the heart, and the digestion of food and framed a comprehensive

theory linking and correlating the phenomena. This theory con-

tained all that Fernel, or any other sixteenth-century physician,knew of the matter. In the first place they discriminated between

three "coctions," the first of which turned the food into chyle,

transported through the veins of the intestine from the stomach to

the liver. This movement of the chyle puzzled Fernel, since he

found the veins full of blood instead of white chyle. In the liver

the second coction transformed the chyle into blood, which issued

forth to the various parts of the body. In these parts the third

coction took place, by which the material absorbed from the

veins by the flesh was made flesh itself. The coctions were assisted,

if not effected, by the natural heat of the animal body, being thus

analogous to ordinary domestic cooking, and each had its specific

cause in a faculty of the soul.1 The nutritive faculty, working

through the natural spirits, was the agent of the first coction; an

attractive faculty drew the blood from the liver along the veins,

and from the veins into the flesh. The liver was the source of the

blood, and the centre from which it flowed out to the parts, in-

cluding the heart. This flow of blood was not constant, but rather

an ebb-and-flow alternating motion, by which the humours were

uniformly distributed about the body. Thus the Ghost in Hamlet

speaks of the

. . . cursed hebenonThat swift as quicksilver it courses throughThe natural gates and alleys of the body.

2

The Galenic theory certainly did not postulate that the blood lay

stagnant in the veins, but references to this ebb-and-flow from the

liver (to which the Latin circulatio was sometimes applied) have

been misinterpreted as allusions to the true circulation (L.

circuitio) of the blood. A principal portion of the output of blood

from the liver passed up the great vein of the body, the vena cava,

1Fernel, however, likens the second coction in the liver to fermentation;

alchemists similarly spoke of the fermentation of metals.* Gates has been interpreted as a reference to the valves, but the alternative

sense of way, path , is equally possible.

EXPERIMENT IN BIOLOGY '37

to the heart, into the right side of which the blood was attracted

by the heart's active dilatation (diastole) (Fig. 7). At the sametime air inspired into the lungs was drawn down the venous artery

(pulmonary vein) into the left side of the heart. During the phaseof contraction of the heart (systole) blood was squeezed from the

right side of the heart into the arterial vein (pulmonary artery) for

the nourishment of the lungs, and also through the median septum(the thick wall dividing the heart into two main chambers, or

Vital Spirit

Right Atrium

Right Ventricle

Arterial Vein

(pulmonary artery)

Venous Artery

(pulmonary vein)

Left Atrium

Left Ventricle

Septum

Liver

FIG. 7. Diagram of the structure of the heart and lungs, illustratingthe Galenic physiology.

ventricles) into the left side of the heart. This was the seat of a

most important operation, for there the blood, already containingthe "natural spirits" supplied by the liver, was further enriched

by taking up "vital spirits" from the air. The blood and vital

spirits were conveyed about the body from the left side of the heart

by the arterial system. Thus the main function of respiration wasto introduce vital spirits into the body via the arteries, and of the

heart to serve as the organ in which this enrichment of the blood

took place indeed enrichment is an insufficient word, for as

venous and arterial blood were distinguished by their colour and

viscosity, as well as by their supposed difference in physiological


function, it was long denied that they could be the same fluid.

The venous, alimentary blood was virtually transmuted by the

addition of vital spirit into the spirituous arterial blood.

Another joint task of the heart and lungs was to ventilate the

blood and relieve it of its sooty impurities passing along the

pulmonary vein and exhaled in the breath. The greater thickness

of the aorta and other principal arteries was explained on the

grounds that their dense walls had to retain the fugitive vital spirit,

but as Harvey emphasized, Galen had not denied that the

arteries contain blood as well as spirit. The arterial pulse, the

expansion and contraction of the vessels, was not regarded as

caused by the similar action of the heart, for Galen judged, as the

result of one misleading experiment, that the "pulsive force" was

transmitted along the walls of the arteries. Ferncl added that if

the arteries were swelled by the pulse of blood from the heart theycould not pulsate simultaneously along their length, as they do.

This belief that the arteries have an active diastole and systole of

their own in sympathy with those of the heart was still credited

by Descartes, even though he adopted Harvey's circulation. ToFernel this active contraction of the arteries also served to squeezethe vital spirit into the surrounding flesh. He also, like JohannGiinther a little earlier, observed that the phases of the heart andarteries are opposite, that when the heart shrinks the arteries

swell, and vice versa. Some experiments on this seem to have been

made by Leonardo. The venous system, arising from the liver,

and the arterial system stemming from the heart were thus

structurally dissimilar, and since the physiological functions of

the blood in the veins and the blood and spirit in the arteries

were also different, they were physiologically distinct also. In

this theory the active phase of the heart's action was its diastole,

by which it drew blood, and vital spirit from the air, to itself.

The Galenical theory was universally adopted by subsequentmedical authorities, and became familiar to the Latin West from

the writings of Avicenna and Averroes long before the originalGreek texts were available or thoroughly understood. Therapeuticdirections drawn from the theory varied, but the basic facts were

common to all. The two chief physiological statements of the

theory: (i) that venous blood nourishes the parts, and (2) that

arterial blood supplies the parts with vital spirits, were of course

beyond the experimental inquiry of the sixteenth century. The


anatomists were, however, able to check upon the agreementbetween the Galenic conception of the blood's motion and the

observed structure of the venous and arterial systems, and of the

heart itself. The operation of the valves in the heart offered no

problem: their opening and closing was perfectly accounted for.

But the density of the septum imposed an act of faith uponGalenical theorists. Berengario da Carpi recorded that the intra-

ventricular pores in the septum were seen with great difficulty in

man. Vesalius, probing the pits of the septum, was unable to find

a passage, and in the first edition of De Fabrica he wrote: 'none of

these pits penetrate (at least according to sense) from the right

ventricle to the left; therefore indeed I was compelled to marvel

at the activity of the Creator of things, in that the blood should

sweat from the right ventricle to the left through passages escapingthe sight.' In the second edition he expressed his failure to discover

Galen's pores even more firmly, and remarked that he doubted

somewhat the heart's action in this respect.1 At least one experi-

ment on the heart is recorded by Vesalius, in which the heart-beat

of a dog was restored after opening the thorax by artificially

inflating the lungs. Some anatomists, however, still maintained

that the passages were easy to find in very young hearts, thoughconcealed in the adult body. Meanwhile, the structures in the

veins, later known as valves, had already been observed byEstienne, and from about 1545 were studied by a number of

anatomists, such as Amatus Lusitanus (1511-68) who dissected

twelve bodies of men and animals at Ferrara in 1547 from which

he derived a wholly false theory of their action. As late as 1603these valves were still misunderstood by Harvey's teacher at

Padua, Fabrizio of Aquapendente.Attention was concentrated, not so much on the motion of

the blood, as upon the physiological function of the heart. If the

sixteenth-century anatomists had visualized the problem of the

ebb and flow of the blood in mechanical terms, as a problem in

1 De Fabrica (1543), Bk. VI, Ch. xi, p. 589; (1555), p. 734: 'However

conspicuous these pits [in the septum] are, none penetrate (according to sense)from the right ventricle to the left through the intraventricular septum; nordo those passages by which the septum is rendered pervious present themselves

to me otherwise than very obscurely, however much they are expatiated uponby the teachers of dissection, because they are persuaded that the blood flows

from the right ventricle to the left. Whence also it is (as I shall also advise

elsewhere) that I am not a little hesitant concerning the heart's function in

this respect,'


hydraulics, the vascular valves would have given them cause to

think more profoundly; but this was a post-Harveian conception.The route of the venous blood to the left side of the heart,

whence it could issue to the arteries enriched with vital spirits,

was however open to discovery. Once the impenetrability of the

septum was granted, such blood could only pass via the pul-

monary artery, the lungs, and the venous artery. This is the

so-called "lesser circulation," which is not a circulation at all,

for those who discovered this path had no notion that any blood

traversed it more than once. It was not, apparently, an original

discovery in which Europe has priority. The lesser circulation

was accurately stated by an Egyptian or Syrian physician, Ibn

al-Nafis al-Qurashi, in the thirteenth century in the course of a

commentary on the Canon of Avicenna, in which it was deduced

specifically from the impermeability of the septum.1 There is no

evidence that his statement was known before very recent years,

so that the sixteenth-century discussions appear to be entirely

independent. It is significant that in two so different circumstances

the same observation elicited the same theory. In Europe the

description of the lesser circulation was first printed by the

Catalan Miguel Serveto in a theological work, Christianismi

Restitutio (1553). Serveto was primarily a theologian and thoughhe practised medicine it is not certain that he had a medical

degree. In Paris he was associated with the young Vcsalius andthe veteran Giinther, who spoke of him as an anatomist second to

none, yet it seems that Serveto's experience in dissection musthave been brief. He was greatly interested in medical astrologyand his whole knowledge of medicine seems to be somewhatintellectual and literary. There is an element of mystery in the

sudden introduction of a physiological heresy into a work that

was almost completely obliterated on account of its religious

heresy and which was probably written (though not certainlywith the passage on the circulation) as much as seven years before

its publication. Serveto had some knowledge of Arabic, and it

has been conjectured that he may have studied Ibn al-Nafis'

text, but it seems unnecessary to postulate that he was less originalthan the thirteenth-century Syrian. Some scholars judge that

Serveto may have been indebted to the Italian anatomists wholater described the lesser circulation in print: others think that

1 On Ibn al-Nafis, cf. Sarton, op. '/., vol. II-2, pp. 1099-1 101.


they were indebted to him. This question of priority is not of

great importance.1

Discussion of the Holy Spirit induced Serveto to write of the

three spirits of the blood, the soul of the body (Harvey also wrote

"Anima ipsa esse sanguis"). He denied that there was any com-munication through the septum of the heart: instead, 'the subtle

blood, by a great artifice, passes along a duct through the lungs;

prepared by the lungs, it is made bright, and transfused from the

pulmonary artery to the pulmonary vein. Then in that vein it is

mixed with air during inspiration, and purged of impurity on

expiration.'

The mixture, he said, takes place in the lungs, where the

spiritual blood is given its bright colour, for the ventricle is not

large enough for such a copious mixture, nor the elaboration of

brightness. He imagined channels connecting the artery and vein

in the lung itself, and argued that the artery was far too large for

the supply of the lung alone. His physiological conceptions were

clearly not very different from those of Galen, save that imbibingof natural spirit by the blood was extended along the pulmonaryvein from the heart to the lung. Serveto did not categorically denythat blood sweated through the septum: nor, on one interpreta-

tion, had Galen categorically denied that some blood might passfrom one side of the heart to the other through the lungs. Such was

Harvey's understanding of his words: 'From Galen, that great

man, that father of physicians, it appears that the blood passes

through the lungs from the pulmonary artery into the minute

branches of the pulmonary veins, urged to this both by the pulsesof the heart and by the motions of the lung arid thorax.' 2

Thoughit may be doubted that such an interpretation was accepted in

the sixteenth century, in Serveto original thinking appears to

emerge tentatively from the ideas of the past. His picture of the

lesser circulation was very different from that of Harvey.The same may be said of intermediate presentations of the same

idea. In spite of the almost complete destruction of Christianismi

Restitutio9there is some record of its being read. It has been argued

that the treatment of the lesser circulation by another Catalan1 For the two arguments, cf. H. P. Bayon: "William Harvey, Physician and

Biologist,*' in Annals of Science, vols. III-IV (1938-9); and Josep Trueta:"Michael Servetus and the discovery of the lesser circulation," Tale Journal ojMedicine and Biology, vol. XXI (

1 948) .

* Robert Willis: Works of William Harvey (London, 1857), p. 44.

i 4* THE SCIENTIFIC REVOLUTION

physician. Juan Valverde, in 1554, is imitated directly from that

of Serveto, since he stated, like Serveto, that the pulmonary vein

contains both blood and air (later, in 1560, he wrote that it

contained a copious quantity of blood). Valverde had studied

under Realdo Colombo from about 1545 at Pisa and Rome;remarking that he had frequently observed the anatomical ap-

pearances with Colombo, he seems to claim no originality for

himself. Colombo in turn had been a pupil of Vesalius, succeedinghim for a short space in the teaching of anatomy at Padua, and it

is possible that the genesis of the idea of the lesser circulation took

place there, and so was made known to Valverde. Colombo

certainly claimed the new idea as his own, and hitherto unknown,in a treatise published posthumously in 1559, which may well

have been written before Valverde's printed in 1556. CertainlyColombo's reasoning on the circulation is superior to any that

had preceded it. He made the plain statement that the blood

passed from the right ventricle through the pulmonary artery to

the lung; was there attenuated; and then together with air was

brought through the pulmonary vein to the left ventricle. He relied

particularly upon the observation that when the pulmonary vein

is opened it is found to be full of bright arterial blood.

From this time the circuit through the lungs from the right side

of the heart to the left was described by a number of anatomists,down to the time of William Harvey. It is important to recognizethat though these physicians are correctly spoken of as precursorsof Harvey (in the sense that this passage of blood through the

lungs played a part in the complete theory of the circulation), the

lesser circulation as ii was understood in the sixteenth centurywas not a complete fragment of the whole Harveian theory.

Harvey understood the lesser circulation in a manner that differed

significantly from that of his predecessors. For him it was the path

by which all the blood in the body was transferred from the venous

to the arterial system: for them it was the path by which a portionof the blood formed in the liver and issuing to the parts becamethe blood-and-spirits of the arterial system. For him the pul-

monary vein contained nothing but arterial blood: for them it

contained blood and air. The lesser circulation of the sixteenth

century was, as Serveto said, a great artifice for by-passing the

impenetrable septum: it led to no other new conception duringmore than sixty years: it did not suggest the general circulation


because it was really not a circulation at all. Galen's physiologywas modified, but not entirely displaced. The heart and lungswere still not perceived as the operative organs in the vascular

distribution and the identity of the arterial and venous blood was

still concealed. The reason for this failure to establish a completeidea of the lesser circulation in the sixteenth century is that the

earlier anatomists were attempting to solve a different problemfrom that of Harvey. They were concerned only to find the route

by which blood and vital spirits entered the arteries in view of

the impenetrability of the septum. Harvey's problem was two-

fold; firstly to account for the function of the valves in the veins

(which, as was realized before his time, obstructed the flow of

blood outwards along the veins), and secondly to dispose of the

targe quantity of blood which he knew must enter the heart. The

novelty of his approach was that it ignored the question of vital

spirits altogether, concentrating upon a wholly mechanical, and

partly quantitative, difficulty latent in the accepted doctrine.

This difficulty had occurred to no one before, because no one haddoubted that the contents of the veins and arteries respectively

were absorbed by the parts which attracted them outwards from

the central reservoirs, the liver and the heart. The early theory of

the lesser circulation was, therefore, useful to Harvey in that, at

the proper stage in the development of his own ideas, the transfer

of blood from the right to the left side of the heart could be fitted

in as a partially complete portion of the puzzle; but that theoryin itself was a. cul-de-sac so long as it was no more than a variation

on Galen's.

Harvey began his medical studies at Padua in 1597, the year of

his graduation at Cambridge at the age of nineteen. He remained

there till 1602. His teacher was Fabrizio of Aquapendente, a late

member of the great Italian school of anatomists and embryolo-

gists. At this time the lesser circulation was by no means universally

accepted, and the valves in the veins were still explained in a

variety of mechanically improbable ways. Robert Boyle, in 1688,

recorded a conversation with Harvey (d. 1657) in which Harveyhad said that he was first induced to think of the circulation bythese valves (of whose existence he must have learnt at Padua) :

... so placed that they gave free passage to the blood towards the heart,

but opposed the venal blood the contrary way: he was invited to

imagine that so provident a cause as nature had not placed so many

i 44 THE SCIENTIFIC REVOLUTION

valves without design, and no design seemed more probable than

that, since the blood could not well, because of the interposing valves,

be sent by the veins to the limbs, it should be sent through the arter-

ies and return through the veins. 1

This doubtless presents a very foreshortened view of the truth,

but it does relate Harvey very definitely to the Italian tradition

(as is obvious in many other ways) and it does also indicate

that Harvey's view of the problem was from the beginning a

mechanical one. The fact that in De Motu Cordis the valvular

action becomes one argument among many does not impugn the

credit of Boyle's statement.

It was natural and fitting that Harvey should have traced the

origin of his discovery to the new anatomy of the sixteenth century,for the whole discussion of the vascular system down to his time

had been based on advances in observation. While the theory of

the lesser circulation was itself framed in accordance with ana-

tomical observation, it had not been examined experimentally,nor did it contain any new physiological interpretation. On both

these points Harvey's discovery marks a distinct advance. Firstly,

he showed that if the vascular system was analysed hydraulically,

considering the heart as a pump, the veins and arteries as pipes,

the valves as mechanical valves, the blood itself simply as a fluid,

conclusive experiments on the flow of blood could be made. For

this purpose he disregarded "spirits" altogether, though he still

considered that the heart (not the lungs) restored a spirituous

quality to the blood. Secondly, he introduced a new physiological

conception in which the arterial blood was revivifying and restora-

tive, while the venous blood was the same fluid returning vitiated

and exhausted to the heart where it received its former virtue

again. Blood, in fact, was not itself the aliment of the parts, but a

vehicle carrying the aliment. Harvey's ideas on this were inevi-

tably vague, and conditioned by the knowledge of his time, but

he did conceive of the blood regaining in the heart its*

fluidity,

natural heat, and [becoming] powerful, fervid, a kind of treasuryof life, and impregnated with spirits, it might be said with

balsam.' As cold precedes death, while warmth belongs to life,

he saw the heart as the 'cherisher of nature, the original of the

native fire' whence new blood, imbued with spirits, was sent

1Boyle: Works, 1772, vol. V, p. 427.


through the arteries to distribute warmth about the body.1 On

the passage of the blood through the lungs, Harvey's promise to

explain his conjectures was not fulfilled: but he indicated that he

thought its function was to temper and damp the blood, to preventit boiling up with its own excessive heat. All Harvey's thought onthe physiology of the circulation is obviously pre-chemical, proto-scientific rather than scientific; it does, however, contain the

important seminal idea that there is an exchange by which

"something" is taken up by the venous blood in the heart (really,

of course, the lungs) and given up by tine arterial blood to the

flesh. Granting the contemporary lack of chemical knowledge, it

is only open to the criticism that, in eulogizing the heart, Harveystrangely overlooked the importance of the fact that venous blood

becomes arterial in its passage through the lungs from the right

ventricle to the left, not in the heart itself. Unable to free himself

completely from the error of his predecessors, he could not quiteattain the conception of the heart as a pump only, adding neither

heat nor spirits nor anything else to the blood passing through it.

Thus Harvey's theory is most perfect in its mechanical aspect,

which was fully supported by experiment. His purely anatomical

evidence held little that was new, except perhaps his study of the

heart as a contractile muscle. He also demonstrated the action of

the vascular valves, and the correspondence of the cardiac diastole

with the arterial systole, more forcibly than earlier anatomists.

Even in anatomy Harvey was successful where his predecessorshad failed, in deducing that a mass of discordant observations was

made consistent on the single hypothesis of the circulation of the

blood; as is most clearly seen in his remarks on the fetal circula-

tion. The existence of an intercommunication between the pul-

monary artery and veins, in the mammalian fetus, that disappearsafter birth was familiar to all anatomists, but no one before Harveyhad correlated this short-circuiting of the lungs with either the

supposed sweating of blood through the septum, or its passage

through the lungs. It was left to Harvey to show that the fetal

circulation avoids the lungs because they are collapsed and

inactive. He is most original and striking when he uses the

comparative method: 'Had anatomists only been as conversant

with the dissection of the lower animals as they are with that of

the human body, the matters that have hitherto kept them in a

1Willis, of). /., pp. 47, 68.


perplexity of doubt would, in my opinion, have met them freed

from every kind of difficulty.'1

His admonition was accepted by a host of biologists in the

later seventeenth century, including Marcello Malpighi who first

observed the blood passing from the arteries to the veins throughthe capillary vessels in the lungs of a frog the final link that

clinched Harvey's motion in a circle. Harvey found that the

action of the heart could be most easily studied through experi-

ments on small animals or fishes, as for instance observing the

effect of tying ligatures about the great vessels, in suffusing or

draining the chambers of the heart. He correlated the single-

chambered heart correctly with the absence of lungs, and the

double-chambered heart with the possession of lungs, pointingout that the right ventricle, which only sends the blood throughthe lungs, is slightly weaker than the left which sends it round the

whole body. By experiment Harvey proved that the heart receives

and expels during each cycle of expansion and contraction a

significant quantity of blood, not a few drops only: by calculation

he proved that, on the lowest estimate of the change in volume of

the ventricles, all the blood in the body passed through the heart

more than once in half an hour. Even this was a generous under-

estimate. In his second group of experiments, Harvey further

demonstrated that the blood moves away from the heart throughthe arteries, and towards the heart through the veins. These

experiments mainly relate to the human subject, and are such as

would naturally suggest themselves to a physician practised in

phlebotomy. Examining the superficial veins of the arm, he

showed that the limb is swollen with blood when the veins are

compressed, and emptied of blood when the arterial flow is

obstructed. He found that the valves in these veins prevented the

flow of blood away from the heart, and that by arterial manipula-tion it was impossible to force blood through them except in the

contrary direction. Blood always filled an emptied vein from the

direction of the extremity. Again, he showed that in the jugularvein the valves were so constructed as to permit a unidirectional

flow towards the heart only, and that therefore their function wasnot (as some thought) to prevent the weight of blood falling downto the feet. The experience of wounds and venesection was cited

by Harvey to the same general effect, and he further alleged1

Willis, op. cit., p. 35.


the experience of physicians as proof that the blood was the

mechanical agent by which poisons or the active principals of

drugs are rapidly distributed about the whole body.It is today far more easy, by taking the truth of Harvey's

arguments and experiments for granted, to regard his doctrine as

an obvious and straightforward deduction from the anatomical

history of two earlier generations, than to appreciate the nature

of the objections against it. As Galileo remarked in another con-

nection, once this discovery was made its proof was easy: the

difficulty was to hit upon it in the first place. Harvey's discovery,like Galileo's, was made at a rudimentary level of science, but

the true measure of the intellectual effort involved is the fact that

the discovery had escaped all previous anatomists, was greetedwith incredulity and scorn, and was not universally acceptedeven within twenty years. It seems likely that Harvey himself hadworked at the problem for at least ten years before he gained the

solution. Some, as he said, opposed him because they preferred to

endanger truth rather than ancient belief. Others thought that

they had discovered technical anatomical arguments against the

circulation; or that only a portion of the blood circulated; or that

venous and arterial blood could not be the same fluid. Even the

basic anatomy of blood-supply to the chief organs of the body(especially the liver) was still doubtful, and its physiological

interpretation barely begun; the capillary circulation, and the

change in colour of blood, were to remain mysteries long after

Harvey's death. His originality was that he preferred to face these

new problems, rather than tolerate longer the inconsistencies of

the old system, but in this he was followed by few contemporaries.As so often in science, one advance was made not by completely

solving an old problem so that no question remained, but by

transposing the problem into an answerable form, creating fresh

problems by the very act of transposition. Harvey asked a question

which, in his precise terms, had perplexed none of his predecessors,and the answer he worked out was important, not only because

it was correct, or because it challenged prevailing ideas, or even

perhaps because it introduced a new kind of scientific inquiry.

Harvey's influence in this last respect was significant (as much in

his book on generation as in De Motu Cordis) but it was not wholly

unheralded, and some of the new methods exploited by later

seventeenth-century physiologists, such as bio-chemical research


and microscopy, were altogether unknown to him. Perhaps the

most important of his achievements was to leave unsolved

problems not blind, impregnable problems, but questions that

could be answered in the way he had himself declared. Just as

seventeenth-century mechanics was based upon the unsolved (or

imperfectly solved) problems left by Galileo, so the experimental

problems of biology were inherited from Harvey.Descartes was not the earliest supporter of the theory of cir-

culation, but he was the first to try to deduce wider implicationsfrom it. He himself practised anatomy, and made anatomical

experiments. He has been accused of plagiarizing from Harvey in

the Discourse on Method what he himself did not fully understand.

But he assigned to "an English physician" the credit for the

discovery of the circulation, and claimed only for himself the

elucidation of the mechanism of the heart. In his Second Disquisition

to Riolan (1649), Harvey had himself commented adversely on the

doctrine of spirits: 'Persons of limited information, when they are

at a loss to assign a cause for anything, very commonly reply that

it is done by the spirits; and so they introduce the spirits upon all

occasions. . . .'

Harvey's attitude to authority seems to have sharpened with

age, and in this passage it seems clear that he meant to take

"spirits" rather as a term in common use, than as having a certain

existence. At any rate he declared that the spirits in blood are no

more distinct from blood than the spirit of wine from wine itself.

Emphatically, in the Method, Descartes sought to eliminate the old

idea of spirits from physiology altogether.1 If the human body

were purely material, lacking rational or sensitive soul, other than

natural heat in the heart (which is compared to the heat offermen-

tation) it would perform all the functions of the human bodyexcept that of thought. Descartes illustrated this deduction by the

motion of the heart, which he imagined to work like a crude

internal-combustion engine. On contraction, a little blood wouldbe drawn into each ventricle, which being suddenly vaporized in

the hot chamber would cause the whole heart to expand and close

the inlet valves. This expansion of the blood would also open the

outlet valves, so that the blood would pass out into the lungs and

arteries, where it would again condense to liquid and the cyclewould be repeated. The heat of the heart, about which Harvey

1 The word was retained, but with a purely chemical meaning.


had written, thus accounted for its purely mechanical cycle of

expansion and contraction. In his speculation on the heart, whichis neither good engineering nor good physiology, Descartes ex-

ceeded Harvey in the functions he assigned to that organ. It

supplied heat to the stomach to concoct food; it completed the

concoction by distilling the blood in the heart 'one or two hun-

dred times in the day' (according to Descartes, the lungs were

the condenser in which the blood was restored to the liquid state) ;

it forced by compression of the blood 'certain of its parts' to pass

through pores specially designed like sieves to admit them into

the various parts of the body where they formed humours; and it

was the hearth where burned a very pure and vivid flame which,

ascending to the brain, penetrated through the nerves (imaginedas hollow tubes) to activate the muscles. In On Man Descartes

developed the theory that the flow of the spirits was controlled in

the brain by the pineal gland, a sort of valve acting under the

direction ofconscious volition. According to Descartes' study of the

physiology of behaviour, volition played a minor part even in man,who was alone capable of abstract thought and true sensation

(that is, sensations capable of objective judgement), and none in the

activity of any lesser creature. He devoted much attention to the

study of motor mechanisms and reflex actions as for instance

tracing the involuntary mechanisms by which, when the handis burnt, the muscles of the arm contract to withdraw it from the

fire, the facial muscles contract in a grimace of pain, tears flow,

and a cry is uttered. 1 He regarded the greater part of bodily

activity as due to mechanical processes of this kind, as automatic

responses to external stimuli effected by the nervous system; but,

though Cartesian physiology was to some extent supported byanatomical investigation of the relations of nerve, brain and

muscle, it was in the main a purely conceptual structure. Descartes

anticipated some of the conclusions of nineteenth-century

physiology without its careful experimental foundation.

Harvey's work was an important step towards a mechanistic

approach to biological problems, containing a tentative challengeto the supremacy of spirits founded on a particular experimental

investigation. Descartes' more comprehensive and more specula-tive writings elevated mechanism to a universal truth, in physicsand biology alike. Soul and material body could have nothing in

1 Cf. De Homine (Leyden, 1662), pp. 109-10. Sherrington, op. cit., pp. 83-9.


common save a single mysterious point of contact: nothing could

be attributed to the soul but thought. The old physiology postu-

lated a variety of non-material souls or spirits each charged with

the management of a set of bodily functions; for Descartes those

functions were the result of mechanistic processes, as much as the

different appearances and movements of an elaborate mechanical

clock. This, he said in the Discourse on Method, would not appear

strange to those acquainted with

the variety of movements performed by the different automata, or

moving machines fabricated by human industry, and that with the

help of but few pieces compared with the great variety of bones,

muscles, nerves, arteries, veins, and other parts that one finds in the

body of each animal. Such persons will look upon this body as a

machine made by the hands of God, which is incomparably better

arranged, and adequate to movements more admirable than is anymachine of human invention.

The body was not maintained alive and active by one or more

life-forces, or spirits, or souls, but solely by the interrelations of

its mechanical parts, and death was due to a failure of these parts.

Therefore, with no non-material factors involved, everything in

physiology was potentially within the range of human knowledge,since no more was required than the investigation of mechanistic

processes, complex and elaborate indeed. This conception of

Descartes' was of course premature, far beyond the scope of the

scientific equipment of his age, and it led to no immediate physio-

logical discovery. Except perhaps in his work on the eye, the

factual content of his biological theory was wholly misleading.But the influence of his general conception upon the anatomyand physiology of the later seventeenth century was profound.On the whole, those who tried narrowly to demonstrate its truth

in particular applications, like Borelli in On the Motion of Animals

(1680), were least successful, and the attempt to apply mechanical

principles to medicine failed. Ultimately the intractability of

nature prompted a return to more vitalistic ideas. On the other

hand Descartes' justification of experimental inquiry in biologywas of permanent value. Terms like

"vital force" might conceal

deep ignorance without endangering the investigation of those

processes through which vital force was supposed to operate. So

long as spirits or the Paracelsian archeus ruled the body, so long as

the functions of its organs had been subject to the influence of the

EXPERIMENT IN BIOLOGY i 5 <

stars and other occult agencies, it had been futile to interpret

physiological phenomena in the light of the purely material

sciences of physics and chemistry. The barrier between organicand inorganic must have remained for ever absolute. Experimentsfrom which the mystery "life" was excluded would have been

useless. To have shown that the transformation of venous into

arterial blood can be effected by oxygenation would have been

irrelevant to a "spiritual" theory of respiration. The dead liver

of a corpse could throw little light on the living liver of a man.Under Descartes' influence, even at the later stage when his

mechanism seemed crude to a degree, all this was changed. Anorgan or a limb could be studied as a part ofthe whole mechanism,a cog in the works. It could be assumed that what was found to be

true of the part in the laboratory must be equally true of the partin the living body; that particular results obtainable from certain

experimental processes when observed in the living specimenmust be produced by similar processes in its own organization. Thebasic axiom of experimental science is that, circumstances being

unchanged, a like cause will produce a like result because the

"cause" releases a chain of events following an unchanging

pattern, If this is not so, then the experimental method of inquiryis not one that can usefully be applied to the problem. It wasDescartes' discovery (ratiocinative, not empirical) that this wastrue of physiological phenomena; it could be assumed, prima facie,

that circumstances were unchanged (e.g. between the living

body and the chemist's vessel), and that since functions were

automativc, like result followed like cause.

The living state was no longer beyond analysis. Descartes'

scientific writings, even more than Harvey's, suggested a host of

inquiries into the nature of physiological process. Those in which

Descartes had been most interested, pertaining to the operationof the nervous system, made little progress before the nine-

teenth century, though the years immediately after his death saw

important work in anatomical neurology. The mechanism of

respiration was tackled more successfully, and a pregnant analogywas drawn between combustion and respiration no doubt owingsomething to earlier ideas of the heart as the seat of heat. From the

members of the Accademia del Cimento through Robert Boyle to

the eighteenth century a series of investigators studied the effect

of placing small animals in vacuo, in confined volumes of air, or of


various"elastic fluids" (gases). It was discovered that in the

vacuum both combustion and respiration were impossible, andthat life ceased. It was discovered that a combustible or an animalconsumed air (the carbon dioxide being dissolved in the waterwhich rose up in the vessel), but not all the air, and that the gas

remaining after combustion ceased would not support life, as

that which was left after respiration ceased would not supportcombustion. It was further discovered that although vessels couldbe filled with

"fluids" that appeared to be air they would not

support life or combustion. Robert Hooke showed (1667) that a

dog could be kept alive by blowing into its lungs with a bellows,even with the ribs and diaphragm removed, from which he con-cluded that the animal 'was ready to die, if either he was left

unsupplied, or his lungs only kept full with the same air; andthence conceived, that the true use of respiration was to dischargethe fumes of the blood.' Other members of the Royal Societysatisfied themselves by experiment that 'the foetus in the wombhas its blood ventilated by the help of the dam'; and that the

foetal circulation depended directly on the maternal.For a time, as Hooke's words suggest, there was doubt whether

the presence of fresh air in the lungs was necessary to remove

something from the blood (the"sooty impurities" of Galen's

physiology) or to add something to it. On this point the investiga-tions of Richard Lower (1631-91), a physician and an experi-mental as well as theoretical physiologist, threw new light.

1 Inhis Treatise on the Heart Lower extended Harvey's discovery anddefended it against the Cartesian perversions: the heart was notcaused to beat by a fermentation of the blood, but by the inflowof spirits from the nerves, and if the nerves were severed the

pulsation stopped. The blood, not the heart, was the source of

heat, and of the activity and life of bodies in this Lower, moreclearly than either Descartes or Harvey, seems to see the heart as

nothing but a mechanical pump. Nor has the heart anything to

do with the change in colour of arterial blood, for this can be

produced by forcing blood through the insufflated lungs of a dead

dog, or even by shaking venous blood in air:

. . . that this red colour is entirely due to the penetration of particlesof air into the blood is quite clear from the fart that, while the blood1 Tractatus de Corde (1669): English translation by K. J. Franklin in Early

Science in Oxford, vol. IX (Oxford, 1932), especially pp. 164-71.


becomes red throughout its mass in the lungs (because the air diffuses

in them through all the particles of blood, and hence becomes more

thoroughly mixed with the blood)

venous blood in a vessel only becomes florid on the surface. Lowerconcluded that the active factor in this transformation of the blood

was a certain"nitrous spirit" (elsewhere called a "nitrous food-

stuff")1 which was taken up by the blood in the lungs, and

discharged from it 'within the body and the parenchyma of the

viscera' to pass out through the pores, leaving the impoverisheddark venous blood to return to the heart. Respiration, therefore,

was a process whose function was to add something to the blood

(Lower remarked that since "bad air" causes disease, there mustbe a communication between the atmosphere and the blood-

stream); but the fuller understanding of the nature of this addition

had to await the chemical revolution of the eighteenth century.The new ideas of blood as a "mechanical" fluid, a vehicle

for carrying alimentary substances, constituents of the air, andwarmth around the body, suggested the new therapeutic tech-

nique of blood transfusion, of which also Lower was a pioneer.The blood had still a semi-magical quality, and as it was thoughtthat "bad" blood could cause debility, frenzy or chronic disease,

it seemed logical to suppose that if the blood of a human patientcould be replaced by that of a healthy animal, an improvementmust result. An Italian who claimed to be the inventor of the

method of transfusion (though he admitted he had never tried

the experiment) even suggested that it would effect a rejuvenationwhich should be the prerogative of monarchs alone. ChristopherWren (1632-1723), when an Oxford student, made experimentson the injections of fluids into the veins of animals, by which,

according to Sprat, they were 'immediately purg'd, vomited,

intoxicated, kill'd, or reviv'd according to the quality of the

Liquor injected.'2Suggestions for transfusions of blood between

animals, and actual attempts to effect it, were made by various

Fellows of the Royal Society in 1665, and Lower went into the

matter thoroughly, successfully reviving a dog which had been

exsanguinated almost to the point of death. Finally, in 1667,Lower performed before the Society the experiment of transfusingthe blood of a sheep into a certain

*

poor and debauched man . . .

1 Sec below, p. 325.2 Thomas Sprat: History ofthe Royal Society (3rd Edn., London, 1 723), p. 3 1 7.


cracked a little in his head/ which the patient luckily survived

without any change in his condition. In this Lower had been

anticipated by the French physician Jean Denys, whose practicesoon after caused the death of a patient, which led to a prohibitionof transfusion in France and the abandonment of the English

experiments. Several accounts of this time describe the violent

reactions produced by the introduction of animal protein into

the human blood-stream, which rapidly proves fatal, and doubt-

less much of the apparent success of these early experiments maybe attributed to the clotting of the blood in the tubes used,

preventing the passage of more than a small amount. Experimentson transfusion were only resumed in the nineteenth century,when the use of animal blood was abandoned. 1

While one important aspect of the expanding experimental

biology of the seventeenth century was the mechanical andbiochemical study of the blood, whose functions figured so largelyin the therapeutical theories of the time, in another the essential

mystery of "life" was no less involved, and was more directly

explored. This was the investigation of generation and the em-

bryonic development of creatures, including man. Just as interest

in the motion and functions of the blood may be traced to its

prominent place in the Galenic theory of humours, so these

embryological researches return in a continuous tradition to the

work of Aristotle. Of William Harvey himself, certainly one of the

greatest embryologists of the seventeenth century, it has been said

that he did not follow the example of some of his predecessorsin departing from Aristoteleanism, but on the contrary lent his

authority to a somewhat moribund outlook.2 On one importantmatter, however, Harvey contradicted Aristotle altogether, he

was sceptical of spontaneous generation, and if he did not coin

the phrase omne vivum ex ovo, it epitomizes his thought. The partial

discredit of spontaneous generation (not complete, for the idea

was revived in the eighteenth century, when it was refuted

experimentally by Spallanzani, and again in the nineteenth

in opposition to Pasteur) was one of the most important changesin biological thought of the time; a first step towards modern

conceptions of the living state. Formerly organisms had been

1 Cf. Geoffrey Keynes: History of Blood Transfusion, 1628-1914 (PenguinScience News 3, 1947).

1Joseph Nredham: History of Embryology (Cambridge, 1934), p. 128.


divided into four distinct groups: (i) those that are generated

spontaneously, (2) vegetative, (3) animal, (4) human. The first

had only, as it were, a share of the "world-soul"; the others were

distinguished according to the "souls" of their class. As long as

these distinctions persisted, founded on fundamental unlikenesses

attributed to the structure of the world-order reflecting disparities

in the original created endowment, it was impossible to approachthe modern conception of life-processes depending upon the

nature and complexity of the physiological functioning of the

organism. To make the generalization that the life-process is

transmitted solely and invariably through specific mechanisms of

reproduction was a necessary first step towards a rational under-

standing of the nature of this process, and the differences between

matter in the living and the non-living state: indeed, there seems

something fundamentally irrational in the supposition that the

organization of the living from the non-living might be fortuitous,

and commonplace at that. The crude, superficial differences

between the life of a plant and that of an animal are at least

capable of recognition; but what meaning could be attributed to

the difference between the life of a spontaneously generatedmistletoe or worm, and that of other analogous forms? Thedoctrine of spontaneous generation had, moreover, become the

refuge for superstitions and fables of the most absurd character,

wholly inconsistent with any serious study of natural history.

Harvey, it is true, wrote in De Motu Cordis that the heart is not

found 'as a distinct and separate part in all animals; some, such

as the zoophytes, have no heart/ and he continued,C

I mayinstance grubs and earthworms, and those that are engendered of

putrefaction, and do not preserve their species,' If this was not

merely a careless phrase Harvey changed his opinion, for in his

later work On the Generation of Animals (1651), he declared:

. . . many animals, especially insects, arise and are propagatedfrom elements and seeds so small as to be invisible (like atoms flyingin the air), scattered and dispersed here and there by the winds; and

yet these animals are supposed to have arisen spontaneously, or

from decomposition, because their ova are nowhere to be seen. 1

Before such a statement could be given real force and meaning,the arts of natural observation, of comparative anatomy, and of

1 Willis* Works of Harvey, p. 321. Harvey, however, did not give up the use

of the term "spontaneous generation.*'


simple controlled biological experimentation must be developed

to, or beyond, the level which they had reached among the

ancient Greeks. Aristotle's biological knowledge was in manyrespects far superior to anything that was available in the sixteenth

century indeed some of his observations were not to be verified

before the nineteenth. It is astonishing to find, for example, that

Aristotle's sensible and penetrating observation of the process of

reproduction among bees which itself was not quite correct

was universally ignored up to modern times, while credence was

given to fabulous tales of their generation in the flesh of a dead

calf or lion which, besides appearing in the works of many Roman

poets and writers on agriculture, were retailed in the sixteenth

century and later by naturalists like Aldrovandi, Moufet and

Johnson, arid by the philosophers Cardan and Gassendi. Even the

relatively simple life-cycle of the frog was a mystery, at least to

academic naturalists.

Harvey had conjectured that in some cases the invisible "seed"

of creatures was disseminated by the wind. The man who set

himself to confute the widespread fallacy of spontaneous genera-tion systematically was Francesco Redi (1626-78), an Italian

physician who worked under the patronage of the Dukes of

Florence and was an important member of the Accademia del

Cimento. 1 His observations and experiments were varied and

numerous, but the most telling were the most simple. Thus he

was able to prove, by the simplest means, that decaying flesh only

generated" worms" when flies were allowed to settle on it; that

the larvae turned into pupae (which he called eggs) from whichhatched flies of the same kind; and that the adult flies which

infested the putrefying material possessed ovaries or ducts con-

taining hundreds of eggs. Generalizing from such results, Redi

pronounced that all kinds of plants and animals arise solely from

the true seeds of other plants and animals of the same kind, andthus preserve their species. Putrescent matter served only as a

nest for the eggs, and to nourish the larvae hatched from them.

However, he had to admit that there were some examples of

generation which he could not explain. Intestinal worms and other

parasites puzzled him, and he failed to discover the cause of the

growth of oak-galls on trees, which was traced later by Malpighi.This led Redi to speculate somewhat loosely on possible perversions

1 See below, p. 189.


in the"life-force" of host organisms which might produce para-

sitic developments. Micro-biology was only coming into existence

at the time when he wrote, and its absence set a natural limit to

the range of his investigations.

Nevertheless, Redi's demonstrations, combined with the later

work of such naturalists as Malpighi and Swammerdam, were

generally regarded as sufficiently cogent against the doctrine of

spontaneous generation. The second half of the seventeenth

century was a period in which, partly through animal and vege-table anatomy, partly through the use of the microscope, and

partly also through experiment, many of the mysteries concerningthe less obvious processes of reproduction were being cleared up.The sexuality of plants, first asserted by Nehemiah Grew, wasestablished experimentally by Camerarius before I6Q4.

1 But if

the general tendency was for the exclusion of pangenesis, the

experimentalists were not inclined to hasten towards a purelymechanistic interpretation. The embryological speculations of

Gassendi and Descartes found few followers. Harvey had written,

'he takes the right and pious view of the matter who derives all

generation from the same eternal and omnipotent Deity, on whosenod the universe itself depends . . . whether it be God, Nature or

the Soul of the universe,5

though this did not prevent his studyingthe phenomena with all attention. Similarly, John Ray in the

Wisdom of God (1693) related his discussion of the fallacy of spon-taneous generation to the fixed, created nature of species. Ray'sworld was a machine in the sense that he doubted from the

cessation of creation on the sixth day the divine institution of

new species (or the endowment of matter with life de novo) but for

him life was transmissible only through the recurring generations

springing from the original ancestors; since the power of livingwas confined to the whole group of creatures extant at anymoment, it could not be born of any conjunction of purelymechanical circumstances.

Despite the limitations in philosophic outlook, which denied to

many experienced naturalists and to Harvey in particular anyvision of the ultimate potentialities of the admittedly crude

1 When his Letter on the Sex of Plants was published. There were ancient and

popular forms of this idea artificial fertilization of the date-palm had been

practised in pre-classical antiquity but it had not acquired any previousscientific validity.


physico-chemical speculations of the time, the history of embryo-

logy offers a useful example of the critical application of observa-

tion and experiment to the consideration of scientific conceptsof a complex order. This was possible for a variety of reasons,

which point to some significant analogies between the situation

in this science, and that in the physical sciences where so much

progress was made. It was important in this branch of biologythat there were ideas to be challenged or confirmed, problemsthat demanded inquiry, far more obviously than in the purely

descriptive departments. What were the respective contributions

of the male and female parents to their offspring? Were the parts

"formed" or did they merely "grow"? What was the function of

the amniotic fluid, or the foetal circulation? How was the embryonourished, or enabled to breathe? Aristotle's systematic account

had attempted to deal with such questions; his exactness in

biological observation and his acuteness in biological reasoningwere examined no less thoroughly in the sixteenth and seventeenth

centuries than were his doctrines relating to the physical sciences.

As Galileo had wielded the method of Archimedes against

Aristotle, so in effect Harvey and Redi applied the methods of

Aristotle as observer against the conclusions of Aristotle as theorist.

In embryology there was as effective a classical tradition to focus

attention on the critical points as in cosmology or mechanics. Ofcourse the strategic gains were far less there was no dramatic

scientific revolution but the tactical advance in method and

analysis was no less real. Though to later minds some of the

questions asked by the seventeenth-century embryologist arc

meaningless, though the teleological cast of his thought has

proved fruitless, the tradition of investigation has continued

unbroken, and some descriptions of observations made at this

time have never been surpassed. The difficulties to be overcome

in any analytical department of biology were far greater than

those which the new mechanics solved, while in addition the

biologist lacked the logical procedures of physical science. Serious

limiting-factors in the development of those subjects were to

disappear only in the nineteenth century : in the late seventeenth,

however, their techniques were greatly enriched by the use of the

microscope, which will be discussed in a later chapter.

CHAPTER VI

THE PRINCIPLES OF SCIENCE IN THEEARLY SEVENTEENTH CENTURY

CONSCIOUS

reflection on the relations between man and his

natural environment can only be a product of an advancedstate of civilization in which abstract thought flourishes.

Greek philosophers seem to have been the first to discuss the

problem, how can reason be most successfully applied to under-

standing the complex phenomena of material things? and in so

doing they introduced the generalizing of ideas that is essential

to science and distinguishes it from the ad hoc solving of practical

problems undertaken in man's struggle with nature. It is generally

agreed that the foundations of scientific knowledge cannot be

settled, or even verified, by the normal processes of science itself.

If such questions are asked as, what is the status of a scientific

theory? or, what is the meaning of the word "explanation" in

science? or, to what extent is science a logical structure? theycannot be answered without transcending the framework of

science. The scientist must have some idea, which is essentially

philosophical, of how he is going to set about acquiring an

understanding of nature before he can apply himself to this task.

He may in practice be entirely uninterested in philosophy, pre-

ferring to regard himself as a compiler of demonstrable facts;

nevertheless, he cannot escape the implications of adopting a

definite scientific method, which teaches him to record particularkinds of facts, by using certain recognized procedures. Thus the

nature of science in different periods has been determined by the

methods employed in collecting facts and reasoning about them,and by the prevailing approach to the study of natural pheno-mena. For example, when the mechanistic philosophy of the

seventeenth century replaced the teleological outlook of earlier

times the change in the character of scientific explanation was

profound: it was no longer sufficient to ascribe the pattern of

events to divine purpose or the necessary conditions for humanexistence.

159

i6o THE SCIENTIFIC REVOLUTION

Consequently, when comparing the scientific achievements of

one epoch with those of another, it must be recognized that the

aims and methods of scientific activity may themselves vary. Thefundamental philosophy of science is neither fixed, nor static, nor

inevitable. It cannot be claimed that any scientific method is

correct, without considering the nature of the objects it seeks to

achieve. Both may be subjected to criticism, for it may be asked

whether scientists have the proper aims, or whether they are usingfit methods; and, indeed, from the thirteenth to the seventeenth

centuries there was continuous and effective criticism of science

from each of these points of view. During the eighteenth andnineteenth centuries, however, there was a tendency for practisingscientists to feel a confident complacency concerning their aims

and methods, and to envelop themselves in an impenetrabledetachment from any attempt to interpret their activities philo-

sophically. They were scientists, devoted to a peculiarly rigorous

pursuit of knowledge, not natural philosophers. They despised

metaphysics and logic. Their limited outlook, and their often

shallow pragmatism, would have been intolerable to the Greek

founders of scientific method.

In essence, the Greek notion of scientific explanation (passinginto the European tradition through the medieval dependence onthe philosophy of antiquity) did not differ from that of modernscience. When a phenomenon had been accurately described so

that its characteristics were known, it was explained by relatingit to the series of general or universal truths. The most importantdistinction between Hellenistic science (including that of the

middle ages) and modern science is in the constitution of these

universals, and the methods of recognizing them with certainty.For Platonists the universal truths were Ideas, the principal task

of their philosophy it cannot properly be called science beingthe elucidation of the ideal world of perfect Forms of which the

tangible world was a clumsy model framed in imperfect matter.

Aristoteleans, on the other hand, denied the separability of Idea

(or Form) and Matter (or Substance), but nevertheless wereconcerned with the processes by which Forms, the generalizationsof their science, were detected in the materials provided by sense-

perception. Phenomena were then explained by comprehendingthem within the a priori scheme ofForms. This procedure required,not additions to the alrearlv hpwtlHprino- variptv nf farf hiit thf

SCIENCE EARLY SEVENTEENTH CENTURY 161

exercise of reason upon the facts requiring organization; thus in

the Physics, for example, proceeding from the known facts of

motion and change, Aristotle discusses the logical meaning to beattached to the idea

"motion/' and then from the idea of motion

deduces the properties ofmoving things. In this method experienceand observation are adduced, less to provide bricks to construct

the fabric of the argument, than to give examples of the author's

meaning. As Aristotle declares in the opening of the Physics:

'Plainly in the science of Nature, as in other branches of study,our first task will be to try to determine what relates to its first

principles,' principles however whose validity was tested by the

rule of reason not that of experiment. As when (to cite the Physics

once more) he denies the existence of a vacuum on the groundthat bodies would move in it at an infinite speed, he makes use of

the logical impossibility of a body being in two places at the sametime. Aristotle derived his universal truths before the applicationof intensive inquiry to the phenomena themselves, a procedurewhich Francis Bacon contrasted with his own inductive method:

There are two ways, and can only be two, of seeking and findingtruth. The one, from sense and reason, takes a flight to the most

general axioms, and from these principles and their truth, settled

once for all, invents and judges of all intermediate axioms. The other

method collects axioms from sense and particulars, ascending con-

tinuously and by degrees so that in the end it arrives at the most

general axioms. This latter is the only true one, but never hitherto

tried. 1

In building up a body of scientific knowledge other series of

steps than those of Aristotle were used by the Greeks. One wasa logical process, akin to that of mathematics, applied wheremathematical analysis of the phenomena was feasible. This beganwith a series of axioms or postulates, defining the conditions of

equilibrium in statics, or the geometrical character of the propa-

gation of light in optics, then deduced the consequences of these

axioms in the same way that the Euclidean geometry of space is

deduced from definitions of point and line. The validity of the

postulates was purely experiential, not deriving from any morefundamental truths, so that should it be found, for instance, that

equilibrium could be produced in other conditions than those

1 Novum Organwn, Bk. I, xix.


envisaged the science of statics would be false or incomplete; andin the same way the validity of their consequences might be

illustrated from experience. Other Greek writers, notably the

successors of Aristotle at the Lycaeum, founded their doctrines

firmly on a discussion of experimental data a method which

Aristotle had used in his biological works. 1 A large group of later

Greek scientists were far from merely speculative in their interests

and confined themselves strictly to the discussion of facts, which

they sought to extend and enrich by experiment and observation.

In this way "the sciences," to contrast them with natural philo-

sophy, came into existence. But their works, though permitting

quantitative comparisons with experience (as in Ptolemy's

astronomy), were fragmentary in scope and did not combine into

a systematic interpretation of the universe as a whole. For this

the middle ages turned to the Aristotle of the Physics and On the

Heaven.

As a consequence of his authority the universal truths of

Peripatetic science, originally formulated by sorting out and

abstracting with the aid of logic the confused information im-

parted by sense-perception, tended to become the unquestionablearbiters of thought. However, though the attempt to rationalize

the phenomena of nature by reference to them might often be

productive of nothing more than intricate mental gymnastics, it

could occasionally lead to a more, factual inquiry. Nor were "the

sciences" of the later Greeks wholly neglected by a line of the

more critical arid heterodox medieval philosophers. Thus arose a

problem of method: how were the fruits of the mathematico-

logical or experiential procedures in investigating nature to

be reconciled with the knowledge gained by deduction from

Aristotle's universals? How did knowledge of a phenomenon, in

terms of its relationship to Aristotle's theory of nature, differ from

knowledge of the same thing in terms of the complete descriptionof the chain of events producing it? The interest of such questionswas doubtless heightened by the technological progress of the

middle ages, which literary men did not disregard. There was

much new knowledge to be systematized (in the field of chemistry,for example), new properties of bodies like magnetism to be

explored. And though the main medieval opinion echoed Plato

1 On Strato, cf. Benjamin Farrington, Greek Science (Penguin Edn., vol. II,

pp. 27-44).


and Aristotle in its definition of knowledge as "understanding"

(passive knowledge) rather than"power to control" (active

knowledge), a minority foreshadowed a less contemplative, more

practical view of science. Yet the evidence for actual experimenta-tion by medieval philosophers is not massive, even in optics, andsome of the warmest advocates of the experimental method, like

Roger Bacon, were guilty of misstatements of fact which the most

trifling experiment would have corrected. More successfully, theydiscussed the intellectual problem of the relationship between

facts and theories, modifying Aristotle's teaching with regard to

the acquisition of knowledge, the nature of causation, and the

character of the proof of a proposition. It has been suggested that

the middle ages witnessed the philosophical development of the

experimental method, through whose systematic application the

dramatic changes of the scientific revolution were effected. 1

Attention has been drawn to the empiricism of such philosophersas William of Ockham, who regarded as "real" only that which

could be perceived by sensation, and to the notion of explainingan event by giving a history of its antecedents, among other signsof the future onslaught upon the foundations of Aristotelean

physics. But traditional ideas continued to satisfy the majorityuntil the seventeenth century, and the philosophic conception of

empiricism was a very different thing from its application to

scientific problems.No important re-statement of scientific method was made

during the sixteenth century. The medieval tradition continued

to run strong, yielding wider divagations from Peripatetic ortho-

doxy in Leonardo or Copernicus, or the philosophers Cardan and

Telesio, but there was no philosopher independent enough to

transfer the weight of scientific authority to completely new bases.

Instead, it may be noticed that a number of the more interesting

developments in the science of the period signify that science was

outgrowing its cradle, philosophy. They bear the mark of the

practical hand of a Vesalius or an Agricola. Since no true science

can remain permanently at the level of simple description, the

first half of the seventeenth century witnessed further efforts at

1e.g., A. C. Crombie: From Augustine to Galileo (London, 1952), p. 217,

etc.: 'The development of the inductive side of natural science, and in fact the

thorough-going conception of natural science as a matter of experiment as

well as of mathematics, may well be considered the chief advance made by the

Latin Christians over the Greeks and Arabs.'


rationalization. Of these two were properly philosophic and

systematic: Francis Bacon aimed at an exclusively experiential

method of scientific inquiry, while Descartes fabricated a new

logical key to nature. The third was Galileo's conscious reforma-

tion ofthe processes of scientific reasoning in mechanics, which was

less a philosophy of science applied to the solving of particular

problems than a reconstruction of a department of science which

necessitated the introduction offar-reaching philosophic principles.

The types of question which a scientist may ask which the

method he uses enables him to formulate, and possibly to solve

may of course be infinitely varied. But here it is useful to single

out two groups among them. The first kind may begin with such

words as "How can we demonstrate that . . .", "How may it be

proved that . . .". These questions are defined, for the investigator

has an idea, however vague, and seeks to test it. The second kind

are undefined, taking such a form as "What are the factors in-

volved in . . .", "What is the relationship between . . .", "Whatare the facts bearing upon . . .". Here the investigator has hardlyarrived at the stage of ascertaining and ordering the relevant facts,

much less examining a hypothesis. Copernicus' problem falls into

the first of these groups, and the problems of seventeenth-century

chemistry and physiology into the second. Part of Bacon's signifi-

cance in the history of science resides in his realization of the

insufficiency of the first aspect of scientific method alone, and

though he made a notable contribution towards it, the second

aspect attracted his main interest. He found the theory of scien-

tific explanation that he encountered insufficient, partly perhapsbecause his education in renaissance humanism gave him little

acquaintance with the natural philosophers of the late middle

ages; but still more warmly, he condemned inattention to the

methods by which the range of scientific facts could be enlarged,or the facts themselves tested and more closely knit together. It

was one of his favourite themes that for many centuries genuinecontributions to solid knowledge had been the work of artisans

rather than of philosophers, of the weavers of speculation. Bacon's

writings have often been described as though his criticisms and

proposals were directly and solely the result of his social sense; as

though, because he believed that progress in material civilization

was a worthy end (a belief shared by both Galileo and Descartes),he reasoned that the single function of science was to enhance


man's command over natural forces. He has thus been depictedas the first philosopher to appreciate the potentialities of science

as the servant of industrial progress. The truth seems to be rather

more complex. It is not even true that Bacon was the first to see

science as a powerful agent in improving material welfare, for this

point had been made by the empiricists ofthe middle ages and was

part of the common descent of magic and science. Nor was Bacon

merely a philosophical technologist; if he wrote

the true and lawful goal of the sciences is none other than this: that

human life be endowed with new discoveries and power,

he also declared, more emphatically, that as

the beholding of the light is itself a more excellent and a fairer thingthan all the uses of it so assuredly the very contemplation of thingsas they are, without superstition or imposture, error or confusion, is

in itself more worthy than all the fruit of inventions ... we mustfrom experience of every kind first endeavour to discover true causes

and axioms, and seek for experiments of Light, not for experiments of

Fruit. 1

Many passages in Bacon's writings indicate that he had a philo-

sophic appreciation of the value of knowledge for its own sake,

not merely for its utilitarian applications. The test by works, in

Bacon's thought, assumed a particular importance not because

works were the main end of science, but rather because they

guaranteed the rectitude of the method used. A discovery or

explanation which was barren of works could hold no positive

merit not because it was useless to man, but because it lacked

contact with reality and possibility of demonstration. Since

Bacon's science was to deal with real things, its fruits must be real

and perceptible.Measured by these standards, Aristotelean science was a hol-

low structure, dealing with abstractions rather than real things,

justified by no fertility in works. Bacon did not deny that there

was truth in the content of orthodox science he was quite as

certain as Aristotle of the stability of the earth but these truths

were buried in a misleading and sterile philosophy. His remedywas to return to a consideration of the bare facts, and above all

to increase vastly the range of facts available. Only when all the

1 Novwn Organum, Bk. I, Ixxxi, cxxix, Ixx.


material upon a particular phenomenon, or natural process, hadbeen collected, classified and tabulated could any general con-

clusions be drawn from it and generalizations be framed. Thefacts might be collected from experience, from reliable reports,

from the lore of craftsmen, but above all from designed experi-

ment. For Bacon clearly conceived of experiment not merely as a

trial "to see what happens," but as a way of answering specific

questions. The task of an investigator was to propose questions

capable of an experimental answer, which could then be recorded

as a new fact appertaining to the phenomenon under study. In

this way the lists of "instances" were to be built up, as Bacon

attempted himself to construct tables of instances of heat andmotion. Other aids were then required in the intellectual processoffinding order in the mass of fact compiled, for which also Bacon

made suggestions. In the New Atlantis the work ofthe fact-gatherers

is separated altogether from the work of the fact-interpreters, andthis has been criticized as a defect in Bacon's system. Yet in

practice in science it has often happened that a new generaliza-tion in theory has interpreted a mass of evidence assembled by a

line of earlier experimental investigators.

Some comments on science have denied categorically that there

is any such thing as a specific "scientific method," by saying, for

example, that science is organized common sense. Bacon's methodat least seems to suffer from excessive formalization and a top-

heavy logical apparatus. Even in his own ventures into scientific

research Bacon did not observe his complex rules very strictly,

and hence the once popular notion that he invented and described

the method of experimental science is no longer acceptable.Modern science was not consciously modelled upon Bacon's

system. Mathematical reasoning especially, so freely and success-

fully exploited from the earliest stages of the scientific revolution,

he never understood so that its essential role was hidden from

him. It has also been said, with less justice, that the integrationof theory and experiment typical of modern research was not

allowed for in his system and that he did not foresee the importanceof hypothesis in the conduct of an investigation. In fact Bacon did

envisage the situation where reflection on the facts suggestsseveral possible theories, and discussed the procedure to be

adopted for the isolation of the correct one by falsification of the

others. And certainly he understood the decisive nature of a


"crucial experiment" in judging the merit ofan idea taking shape

in the investigator's mind. It should not be forgotten, too, that

pure fact-collection (the first stage in Bacon's system) has been a

most important fraction of all scientific work up to the presenttime. Even the routine verification of measurements, or the

establishment of precise constants, has been productive of originaldiscoveries. It is true that the main course of physical science in

the seventeenth century ran in a very different direction, that

in the new mechanics of Galileo the plodding fact-gathering

imagined by Bacon had' little significance; elsewhere in science,

however, where the organization of ideas was less advanced andthe material far more complex and subtle, the straightforward

acquisition of accurate information was a more fruitful endeavour

than premature efforts at conceptualization. This is most

clearly true of the biological sciences; no Galileo could have

defined the strategic ideas of geology or physiology which only

emerged from the wider and deeper knowledge of facts obtained

in the nineteenth century. Bacon's advice that solid facts, certified

by experiment, should be collected and recorded was sound and

practical; this task occupied chemistry and biology till towards the

end of the next century. But in the long run the great generaliza-tions in these fields did not follow from the kind of digestion andsublimation of fact that Bacon had described.

While Bacon's works gave a useful impetus to the growinginterest in science, especially in England, his attempt to define

the intellectual processes involved in the understanding of nature

was limited and only partially helpful. Empiricism alone is aninsufficient instrument in science. The history of the scientific

revolution shows the fertility of the critical examination of con-

cepts and theories, even when the modification of the simpleaccount of the facts is insignificant (as with Galileo's new conceptsof inertia and acceleration). Bacon's views were characterized byhis approach to science, which was that of a philosopher rather

than that of an experienced investigator. His own ventures in

research are notoriously uninteresting and unproductive, for

except in his leaning towards an atomistic materialism he was out

ofsympathy with the progressive ideas ofthe time, and remarkablyindifferent to those developments which posterity has found most

significant. His logical system was for the most part ignored bythose who were finding how to make discoveries regardless of


logical systems, and consequently modern science did not so much

grow up through Bacon as around him.

Galileo offers a very different picture. On the one hand he was

mainly occupied with purely scientific matters and the discussion

ofspecific problems. He did not construct a methodical philosophyof science, though the elements of such a philosophy may be

extracted from his works. On the other hand he may properly be

described as a philosopher, for his conscious reflection on the

obstructions to be overcome in arriving at a clear and confident

understanding of nature is explicit in a number of passages and

implicitly conditions the revolution in ideas that he effected. Like

other major critics of Aristotle, Galileo was faced with two

inescapable problems: on what foundations was the intellectual

structure of science to be built, and what criteria of a satisfactory

explanation were to replace those of Aristotle? With Galileo these

questions were not answered in prolonged metaphysical or logical

analyses though it seems clear that his ideas were shaped by just

such analyses carried out by his predecessors but the answers

were given as they became necessary in the progress of his attack

on the prevailing ideas of nature. As scientist Galileo's aim mightbe to detect Aristotle's errors in fact or reason, while as philo-

sopher he demonstrated more fundamentally how these errors hadarisen from weaknesses in method that were to be avoided bytaking a different course. The negative exposure of an isolated

mistake by means of experiment or measurement was not, in

Galileo's view, the sole advance of which the new philosophy was

capable.Galileo's two greatest treatises are polemics. They do not relate

how certain conclusions were reached, instead they seek to provethat these conclusions are certainly true. Their arguments are

therefore synthetic, and the texture of reasoning and experienceis so woven that experience appears less as a peg upon which a

deduction depends, than as an ocular witness to its validity. It is

universally the case that the methods by which a discovery is

made and expounded differ, in varying degrees, and Galileo

rarely used the direct technique of reporting and inference, so

much favoured later by the English empiricists. In the Dialoguesand Discourses the foundations of scientific knowledge are shown to

reside in phenomena and axioms conjointly. By its attention to

actual phenomena Galilean science was made real and experien-


tial; by its use of the capacity of the mind to apprehend axiomatic

truths its logic was made analogous to that of mathematics. Thelatter were indeed generalized from the former, but the process

might involve historical as well as philosophical elements. Thusa fundamental axiom of the Dialogues is that heavenly bodies

participate in uniform circular motion, while in the Discourses

successive propositions in dynamics are deduced from the axio-

matic definition of uniform acceleration. Such axioms, illustrated

and confirmed by experiment, become the starting-point for

arguments through which their implications are unfolded (in the

manner of Euclidean geometry or Archimedean statics) and againin turn verified by experience, or applied to specific problems,such as the isochronism of the pendulum.

Galileo's remarks on the procedure to be adopted in arriving at

these principal generalizations are therefore of special interest.

The most important step is that of abstraction. The essential

generalizations are not to be taken as the end-product of the

logical examination of an idea, in the manner of Aristotle, but

are obtained by abstracting everything but the universal element

in a particular phenomenon, or class. So far Galileo agrees with

Bacon, though he offered no comparable set of logical rules for

effecting this operation. He went on, however, to insist emphati-

cally that by abstraction it is learnt that the real properties of

bodies are purely physical, that is, size, shape, motion, propin-

quity, etc., not colour, taste or smell so that as he stated in the

Saggiatore, the "accidents, affections and qualities" attributed to

them are not inherent in the bodies at all, but are names given to

sensations stimulated in the observer by the physical constitution

of that which he perceives. Galileo noted that this failure to ab-

stract from sensations to the underlying physical reality had givenrise to much confusion in the study of heat; physically considered

(he says) there is no mystery in heat, which is merely a name

applied to a sensation produced by the motion of a multitude of

small corpuscles, having a certain shape and velocity, whose

penetrations into the substance of the human body arouse such

sensation. 1 In these opinions the influence of Epicurean atomismis evident; one might say that this whole approach to the question

1 // Saggiatore (Bologna, 1655), pp. 150-3. Bacon also agreed that 'heat is

an expansive motion restrained, and striving to exert itself in the smaller

particles.' (Novwn Organwn, Bk. II, xx.)

lyo THE SCIENTIFIC REVOLUTION

ofprimary and secondary qualities is determined by a mechanistic

notion ofthe composition of matter. The explanation ofa scientific

problem is truly begun when it is reduced to its basic terms of

matter and motion the transformation which remained the ideal

of classical physics. The name heat could not be a cause, since as

Galileo pointed out there is nothing between the physical pro-

perties of bodies with the varying motions and sizes of their com-

ponent particles and the subjective perceptions of the observer.

He found other instances in conventional science of this tendencyto believe that matters could be explained by juggling with

abstract names, as when in the Dialogues gravity is defined as onlythe name of that which causes heavy bodies to fall; naming does

not contribute to understanding. Of course Galileo did not meanthat there is no purpose in classifying phenomena; his argumentis that classifications based on superficial characteristics and naive

analyses are misleading because they conceal physical realities.

They had concealed the universal generalizations on motion,whether caused by gravity or any other force, which it was

Galileo's main achievement to reveal.1

In the process of abstraction an important aid was mathematics.

If the elements of a problem were capable ofstatement in numeri-

cal terms then the most exact definition had been framed and the

most general case considered. Moreover, by transposition into

mathematical language the conditions of the problem could be

exactly prescribed, in order to remove the imperfections andminor variations that always occur in actual experience. As in

geometry the areas of triangles can be calculated more preciselythan they can be measured, so in mechanics the properties of the

lever, the inclined plane, the rolling sphere could be calculated

by reducing these physical bodies to geometrical forms whosebehaviour could be established by abstraction from that of their

physical counterparts. Galileo knew that this was a function of the

imagination; a calculus may solve a problem, but the due con-

ditions must be postulated before the calculation can begin. Themotion of a perfect sphere on a perfect plane must be inferred

imaginatively from the motion of physical spheres on physical

planes, or the motion of an ideal pendulum from that of actual

1Similarly, a chief problem of the early botanical taxonomists was to

penetrate below the superficial differences and similarities in plants to more"real" morphological distinctions.

SCIENCEEARLY SEVENTEENTH CENTURY 171

oscillating bodies, but this, for Galileo, was strictly analogous to

Euclid's abstraction in the definition of space, or Archimedes'

assuming that the cords hanging from the ends of a balance are

geometrically parallel. Mathematics, serving as a guide to the

imagination as well as handling the abstracted properties, could

yield further statements which, through reference to experience,

might confirm the process of abstraction and the generalizationsderived from it. In this ideal world of abstraction, without

resistance or friction, in which bodies were perfectly smooth and

planes infinite, where gravity was always a strictly perpendicularforce and projectiles described the most exquisitely exact para-

bolas, the principles of Euclidean geometry held absolutely. Theworld of Galileo's imagination in mechanics was in fact Euclid's

geometrical space with the addition of mass (later defined pre-

cisely by Newton), motion and gravity. The secret of science, in

Galileo's outlook, was to transfer a problem, properly defined, to

this abstracted physical universe of science which, as ever greater

complexities are added to it, approximates more and more closelyto the actual universe. For the architecture of the real world is noless mathematical than that of Euclidean space, the book ofnature

being written 'in mathematical language . . . the letters [being]

triangles, circles and other geometrical figures, without whichmeans it is humanly impossible to comprehend a single word.'

As Galileo elsewhere declared, there is no distinction between

"real truth" and mathematical truth. On this account he has

been called a Platonist, whereas perhaps he was rather a Euclidean

in mechanics, never cultivating the mathematical mysticism that

distinguished Kepler. Moreover, Galileo recognized that while

mathematical logic is infallible, it may rest on false assumptions,like those of the Ptolemaic system, which 'although it satisfied an

Astronomer meerly Arithmetical, yet it did not afford satisfaction to

fhe Astronomer PhylosophicalS It was but too easy to mistake one

of nature's circles for a triangle.

By the method of abstraction, moreover, the scientific conceptof "laws of nature'

1 was simply and neatly accommodated. This

concept, unknown both to the ancient world and to the Far

Eastern peoples, seems to have arisen from a peculiar interaction

between the religious, philosophic and legalistic ideas of the

medieval European world. It is apparently related to the conceptof natural law in the social and moral senses familiar to medieval

iya THE SCIENTIFIC REVOLUTION

jurists, and signifies a notable departure from the Greek attitude

to nature. The use of the word "law" in such contexts wouldhave been unintelligible in antiquity, whereas the Hebraic andChristian belief in a deity who was at once Creator and Law-giverrendered it valid. The existence of laws of nature was a necessary

consequence of design in nature, for how otherwise could the

integrity of the design be perpetuated? Man alone had been given

free-will, the power to transgress the laws he was required to

observe; the planets had not been granted power to deviate from

their orbits. Hence the regularity of the planetary motions, for

example, ascribed by Aristotle to the surveillance of intelligences,

could be accounted for as obedience to the divine decrees. TheCreator had endowed matter, plants and animals with certain

unchangeable properties and characteristics, of which the most

universal constituted the laws of nature, discernible by humanreason. This conception is clearly capable of association with a

mechanistic philosophy, and irreconcilable with animism; as

Boyle put it:

God established those rules of motion, and that order amongst things

corporeal, which we call the laws of nature. Thus, the universe beingonce framed by God, and the laws ofmotion settled, the [mechanical]

philosophy teaches that the phenomena of the world are physically

produced by the mechanical properties of the parts of matter. 1

If this transcendental status be granted to the laws of nature-so that one may inquire what they are, but not why they hold

the question may still be asked, "How may a given propositionbe recognized as a law of nature?

"In other words, how does a law

of nature differ from any other generalization which happens to

be true because no instance to the contrary has yet been dis-

covered? Modern philosophers of science, having deprived the

laws of nature of their transcendental status, present their ownanswers to this problem. Galileo, and after him Newton, obtained

an answer to it by application of the method of abstraction. WhenGalileo created by abstraction the essential model of the pheno-mena of motion which he studied, he transformed the pragmatic

validity of a generalization appropriate to the world of experienceinto the absolute validity of the law of nature in the intellectual

1 The Excellence and Grounds of the Mechanical Philosophy, in Philosophical Works,

abridged by Peter Shaw (London, 1725), vol. I, p. 187 (condensed).


model. Thus Newton, following Galileo, formulated his laws of

motion as laws of nature having complete applicability within the

fabric of mathematical physics, whose conclusions as a whole can

be confirmed by direct observation. In this way the difficulty that

the perfect universality of the laws of nature cannot be established

by experience of countless instances was overcome. For Galileo

and the later scientists who adopted his method such laws had a

greater force than descriptive generalizations could attain, because

they had acquired a fundamental systematic status in the scientific

picture of the universe.

Hence laws of nature could be considered in theory as being

rigorously exact, although the ascertainable correspondence be-

tween laws and experience in the physical world is limited byprobability-factors in experiments and by the intervention of a

multitude of complications. Such limitations were discovered, for

example, by the early experimenters in mechanics who discovered

that Galileo's theorems on motion could not be rigorously con-

firmed when applied to the movements of physical bodies. Galileo

had clearly appreciated the exceptional usefulness of the conceptof laws of nature in which they were taken to represent that whichthe intellect, aided by scientific abstraction, conceives as the

essence of certain phenomena, but it fell to others to demonstrate

more satisfactorily the precautions which the scientist must take

in relating the laws to the crude evidence of the senses.

When abstraction has played its part, when attention has been

given to the really existing physical properties of bodies, when the

mathematization of the phenomena has been fully explored and'a theoretical science begins to take shape, how is the investigator

to determine whether his image or model of things in the ab-

stracted universe represents faithfully things as they are accordingto experience? Galileo's answer to this problem, prepared for him

by earlier logicians, was the appeal to experiment. If theoretical

examination suggests that in specified conditions the event B will

follow the event A, then the reasoning can be tested by creatingthose conditions, and making the observation. This doctrine is not

explicit in Galileo's writings, but it is implicit in their texture.

Thus the difference between Galileo and Bacon in this respect is

that the former emphasized mainly the role of experiment in test-

ing a theory, or determining its constants, while the latter stressed

the r61e of experiment as a means of obtaining information. In


Galileo's view the questions which the investigator can ask nature

are most useful when they are not random questions, but are so

designed that a single unambiguous response can be elicited from

the experiment. This is probably the cardinal feature of modernscientific method, of which numerous examples are to be found in

Galileo's writings, such as the use of the experiment with the in-

clined plane to verify the law of acceleration. It would be erroneous

to suppose that it had never appeared in earlier scientific research,

but it is with Galileo that it becomes its main pillar. It must be

observed, however, that the experimental method is capable of

bearing different connotations. With Bacon the appeal to experi-

ment is a remedy for ignorance:

Let further inquiry be made as to the comparative heat in different

parts and limbs of the same animal; for milk, blood, seed and eggsare moderately warm, and less hot than the outward flesh of the

animal when in motion or agitated. The degree of heat of the

brain, stomach, heart, and the rest has not yet been equally well

investigated.l

With Galileo experiment is a test of knowledge, confirming a

necessary deduction in the development of a sound theory, so that

he can even declare:"If you were to perform such an experi-

ment then you would obtain such a result," although he has never

made the experiment himself. Or in other passages he refers to

his readers' experience of the reflection of light from mirrors, the

motion of bodies in a ship under way, the passage of fluids between

vessels; a possible experiment is described, but none is reported

circumstantially. The function of these"thought-experiments

5 '

in the argument of the Dialogues or Discourses is not to demonstrate

a new fact so much as to guide the imagination into perceiving the

agreement between experience and the ideas put forward. AsGalileo had framed his concepts, not in the laboratory but by a

correct analysis ofthe common evidences ofmotion, so in exposition

reversing the process he teaches the reader to analyse his own ex-

perience of motion by means of these thought-experiments. Hewas well aware that experimentation is a double-edged weapon,deceiving those who use it crudely, as when he writes of the

"sublime wit" of Copernicus, whodid constantly continue to affirm (being perswaded thereto by reason)that which sensible experiments seemed to contradict; for I cannot

1 Novwn Organum, Bk. II, xiii.


cease to wonder that he should constantly persist in saying, that

Venus revolveth about the Sun, and is more than six times further

from us at one time, than at another; and also seemeth to be alwayesof equal bigness, although it ought to shew forty times bigger whennearest to us, than when farthest off.

1

Sheer empiricism, therefore, could not uncover physical reality,

which could only be glimpsed through the alliance of analytical

reasoning (especially ofthe mathematical kind), scientific imagina-

tion, and experimental caution.

From the critique of empiricism it emerges that in Galilean

science experiment is incompetent to confirm the whole intellectual

structure, whose conceptual elements transcend experiment. For

example, the concept of acceleration which science owes to Galileo

cannot be proved in the laboratory, though its applicability in

representing phenomena can be illustrated. For the definition of

acceleration involves the further concepts of time and velocity, the

latter a function of time and the concept distance. There is perio-

dicity in nature, and there are intervals in nature, but nature offers

no ready-made dimension-theory embracing the concepts of time

and distance. These can have no other status than that of ideas or

mental constructs which help to form the world-picture, havingthe advantage that unlike concepts of beauty and justice they can

be understood in the same sense by all men. But their definition is

of mind, not innate in the fabric of the universe. The concept time

gives order to certain kinds of experience, the concept distance to

others, and from these arise velocity arid acceleration rationalizingothers still, so that the first test for a definition of acceleration mustbe its assimilability in logic to existing dimension-theory; more-

over, in a second test, by experiment, the usefulness of the newconstruct cannot be distinguished from the usefulness of the exist-

ing constructs, time and distance, so that effectively the whole

system of constructs must be tested together, if at all. Though the

Galilean scientist seeks to penetrate ever deeper into physical

reality, the nodes of his exposition of nature can never be morethan mental constructs, time, acceleration, the chemical element,or the electron, which give order and significance to the experi-

mental data. This incidentally provides the justification for

Galileo's thought-experiments; the constructs are equally valid

when they give order to the facts of experience, duly analysed, as

1Dialogues (trans. T. Salusbury), p. 306.

iy6 THE SCIENTIFIC REVOLUTION

when they apply to the most delicate determinations of the

l^t^oratory.

If the theoretical part of science, leaving aside its practical

success in operating with materials and instruments, is a frame-

work of mental constructs giving order to experience, then it

follows that the only kind of explanation that is possible is one

that arranges the constructs in a logical pattern; as when the

properties of the molecule are traced to its atomic structure, andthe properties of the atom to its electrons. The sole method of

assigning a cause to any particular phenomena is to invoke the

constructs applicable to it, that is, the generalizations derived

from the study of less complex phenomena. In this way Galileo

used his concepts of motion to describe and account for the tra-

jectory of a projectile, as a modern physiologist more elaboratelyuses the concepts of cytology, biochemistry and even the physicalnotions of matter and energy to describe and account for the

functioning ofa part ofthe body. That it is never possible to touch

any cause more fundamental than a construct or generalizationderived from the description of some definite phenomenon, andthat therefore explanation and description have no really distinct

significance in science, was the great methodological discovery uponwhich the scientific revolution flourished. In Galileo's works its

full powers appear for the first time, but it was only graduallyextended from mechanics to the non-physical sciences. In the Dis-

courses (Third Day) Galileo disposed of the causes of the accelera-

tion of freely falling bodies imagined by philosophers as fantasies

unworthy of examination: 'At present it is the purpose of our

Author merely to investigate and to demonstrate some of the

properties of accelerated motion (whatever the cause of this

acceleration may be).' This does not mean that in replacing the

question why by the question how Galileo has excluded the studyof phenomena in terms of cause and effect it was his pupilTorricelli who proved that the cause of the horror vacui (so called)

was the pressure of the air. Mere simple description, like that of

anatomy, was not the sole end of the new sciences Galileo created,for the formulation of constructs and generalizations is a necessaryfeature of the full description of a class of events, e.g. accelerated

motion. Galileo seems rather to be making the minor point that

if the cause of B is called A, the first subject of study must be Bitself (since it is from B that the very existence of A is wholly or


in part inferred), and the more serious point that to describe andaccount for the A-B relationship, the investigator must be able to

make a number of statements concerning A independently of Bin order to establish its character. In other words, since causation

and full description are synonymous, the"cause" ofB (accelera-

tion) is a property ofA (gravity), not of B, and can be sought onlyin the description of A. This is Galileo's attitude throughout the

Discourses, as it is Newton's throughout the Principia. The explana-tion ofphenomena at one level is the description ofphenomena at

a more fundamental level, that is, one nearer to the primaryrealities of classical physics, matter and motion.

Following the example of Galileo, the scientist may as it were

work either upwards or downwards; he may seek for a morefundamental construct (like the law of inertia, or the laws of

thermodynamics) or he may examine the applications of the con-

struct to the details of a complex phenomenon (like the isochron-

ism of the pendulum). In either case he may have to handle

constructs which are not reducible to the ultimate physical reali-

ties, as was the case for instance with Newtonian mechanics where

the law of gravitation had to be taken as descriptively correct,

though gravity was not explicable in terms of matter and motion.

For Galileo there was no anomaly in recognizing that certain

constituents of the physical world had to be accepted as axio-

matic; descriptive analysis can only advance gradually from the

coarse to the refined, from the lower to the upper levels, each with

its appropriate generalizations. In the period between Galileo and

Newton, however, the validity ofthe purely descriptive generaliza-tion (which rests upon scepticism concerning the possibility of

arriving at a final indubitable truth serving as the single origin of

scientific thought) was challenged in the philosophy of Descartes,

and rejected by the systematists who expounded Cartesian ideas.

The chief difference between Galileo and Descartes lay in this,

that while the former believed that a body ofknowledge successful

in organizing sense-perceptions (duly refined and analysed) andin framing generalizations based on them gave an adequate under-

standing of nature, the latter believed that there was no reliable

test of the significance of sense-perceptions other than that which

issues from a deeper metaphysical certainty. The mind, being

extra-nature, was capable of doubting anything external to itself

in nature.


As Descartes relates in the Discourse on Method (1637), after

completing a thorough education, in which,'

not contented with

the sciences actually taught us, I had read all the books that hadfallen into my hands, treating of such branches as are esteemed

the most curious and rare,' he found himself involved in manydoubts and errors, persuading him that all his attempts at learninghad taught him no more than the discovery of his own ignorance.In philosophy, despite all the efforts of the most distinguished

intellects, everything was in dispute and therefore not beyonddoubt, and as for the other sciences 'inasmuch as these borrow

their principles from philosophy,' he reasoned that nothing solid

could be built upon such insecure foundations.

In this perplexity, Descartes proposed to himself four "laws of

reasoning" which he applied in the first place to the study of

mathematics:

In this way I believed that I could borrow all that was best both in

geometrical analysis and in algebra, and correct all the defects of the

one by the help of the other. And, in point of fact, the accurate ob-

servance of these few precepts gave me such ease in unravelling all

the questions embraced in these two sciences, that in the two or three

months I devoted to their examination, not only did I reach solutions

of questions I had formerly deemed exceedingly difficult, but even as

regards questions of the solution of which I remained ignorant, I wasenabled as it appeared to me, to determine the means whereby, andthe extent to which, a solution was possible.

Mathematical ideas, then, could be understood with perfect

clarity and mathematical demonstrations accepted with absolute

confidence. These principles, to which Descartes held firm in all

his scientific activities, allyhim with Galileo in the attainment ofthe

ideal of mathematization throughout science. Indeed, Descartes'

most valuable contribution to the scientific revolution was the

co-ordinate geometry described for the first time in the samevolume as the Method. But his grasp of a starting point for the

comprehension of fact, rather than the abstractions of mathe-

matics, depended upon a form of psychical crisis from which he

emerged possessed with the metaphysical force of the statement,/ think, therefore I am:

I thence concluded that I was a substance whose whole essence or

nature consists in thinking, and which, that it may exist, has no need

of place, nor is dependent on any material thing; so that "I," that is


to say the mind by which I am what I am, is wholly distinct from the

body, and is even more easily known than the latter, and is such, that

although the latter were not, it would still continue to be all that is.

This led Descartes to inquire why he had found Cogito, ergo sum

an infallible proposition, whence he convinced himself that all

things clearly and distinctly perceived as true, are true, 'only

observing that there is some difficulty in rightly determining the

objects which we distinctly perceive.' Further, he declared that

since the mind is aware of its own imperfection, there must be a

being, God, which is perfect and that since perfection cannot

deceive, those ideas which are clearly and distinctly perceived as

true are so because they proceed from perfect and infinite Being.So much more certain are the fruits of reason, says Descartes, that

we may be less assured of the existence of the physical universe

itself, than of that of God, 'neither our imagination nor our senses

can give us assurance of anything unless our understandingintervene . . . whether awake or asleep, we ought never to allow

ourselves to be persuaded of the truth of anything unless on the

evidence of our reason.'

After this denunciation of empiricism, this declaration that .all

knowledge of truth is implanted by God, this assertion that the

task ofthe scientist is to frame propositions as clearly and distinctly

true as those of geometry, what suggestions can be made for the

deciphering of the enigma of nature? According to Descartes, it

is necessary to follow exactly that procedure which Bacon hadcondemned in Aristotle, that is, to establish the prime generaliza-tions that are 'clearly and distinctly true.'

I have ever remained firm in my original resolution ... to acceptas true nothing that did not appear to me more clear and certain than

the demonstrations of the geometers had formerly appeared; and yetI venture to state that not only have I found means to satisfy myselfin a short time in all the principal difficulties which are usuallytreated of in philosophy, but I have also observed certain laws estab-

lished in nature by God in such a manner, and of which he has im-

pressed on our minds such notions, that after we have reflected

sufficiently on these, we cannot doubt that they are accuratelyobserved in all that exists or takes place in the world.

Thus the science of Descartes is a centrifugal system, workingoutwards from the certainty of the existence of mind and God to

embrace the universal truths or laws of nature detected by reason,

i8o THE SCIENTIFIC REVOLUTION

and then from the "concatenation of these truths" revealing the

mechanisms involved in particular phenomena. It is systematic,

unlike the "new philosophy" of Bacon or Galileo, because its aim

is not to enunciate a correct statement here and there as it becomes

accessible to intellect, but to provide an unchanging fabric whose

relevance to particulars is the sole remaining subject of inquiry.

In this respect, despite his contempt for scholasticism, Descartes

sought for himself the commanding authority of a new Aristotle.

Indeed, among Cartesian scientists, and still more among Car-

tesian philosophers of later generations, a new scholasticism

flourished through the dissection, embroidering and expansion of

Descartes' doctrines, until they, like Aristoteleanism in the six-

teenth and seventeenth centuries, were in turn regarded as a

bulwark against dangerous innovations and as the philosophic

justification of religious orthodoxy.1

Apart from his researches in optics and mathematics by far

the portion of the whole which proved of greatest value to science

Descartes preferred to express his ideas in the form of a model,whether of a man or of the universe. Superficially this procedureseems to resemble the Galilean process of abstraction, but in

reality it is very different. Having settled his principles, Descartes

believed that to philosophize about mathematical abstractions

was to promote delusions; his object was the real world, but as he

did not know from experience what the mechanisms of the real

world, or the actual human body, are, he was forced to imaginewhat they must be to accord with the principles and such know-

ledge as he had. He did not claim that in describing the model he

was describing the real world, only that from the identity of their

properties the real world could be understood in terms of the

model. Its mechanism was absolute, since it followed from the

dualism of mind and matter that all the phenomena of nature

resulted from the properties of matter, especially its motion, whichin turn were fixed by natural law. The laws of nature, includingthe definition of matter by extension and the impossibility of a

vacuum, the law of inertia, and the laws of impact between

particles, were derived by Descartes as ideas 'clearly and dis-

tinctly perceived to be true.' Thus Descartes and Galileo agreedthat the only physical reality which science can study is that of

matter in motion; unlike Galileo, however, Descartes did not1 Cf. A. G. A. Balz: Cartesian Studies (New York, 1951).


hesitate to extrapolate far beyond the limitations of mathematical

analysis or experimental inquiry. In the end, elaboration of the

principles, guided only by the criteria of "clear and distinct,"

yielded in Cartesian cosmology, chemistry and physiology

nothing other than subtle scientific fantasy.

Again, with regard to the functions ofexperiment Descartes andGalileo adopted antithetical positions. The pillars of Cartesian

science were "clear and distinct" ideas formulated as laws of

nature; it was to fit these, and not experimental evidence, that its

subsidiary theories were shaped. It was essentially deductive from

these natural laws, and if knowledge did not supply the requisite

materials, then they had to be invented with the aid of reasoned

deduction, as the celestial vortices carrying the planets about the

sun, the three kinds of matter and the variously contrived poresof substances were invented in accordance with the exigencies of

experience and reason. Of course, experience was respected in the

sense that Descartes sought to explain in his model the sum of the

phenomena of nature as he knew them, for it is obvious that he

could not have deduced magnetism within his system had he not

known of its manifestations. But Descartes made no attempt to

confirm his mechanisms in detail by experiment. The foundations

of knowledge, he thought, were best settled without it:

for, at the commencement, it is better to make use only of what is

spontaneously represented to our senses, and of which we cannotremain ignorant, provided we bestow on it any reflection, however

slight, than to concern ourselves about more uncommon or recondite

phenomena; the reason for which is, that the more uncommon often

mislead us so long as the causes of the more ordinary remainunknown. . . .

Experiments indicating some conclusion detached from a deduc-

tive system Descartes distrusted; hence nothing that Galileo did

had value for him, because Galileo did not know the cause of

gravity. This must not be taken to mean that either Descartes or

his successors were totally blind to the merits of experimentation,

though it could only be an adjunct when the application of clear

and distinct ideas failed, or in an obscure inquiry. In his own

experimental researches Descartes revealed great talent, and those

who were influenced by him, like the Dutch physicist Christiaan

Huygens, included some of the great exponents of experimentalscience of the later seventeenth century though indeed they owed


much less in this respect to Descartes, than to the empirical temperof the age, and the emulation of Galileo's example in mechanics.

It was Huygens who later described Descartes as the author of

*un beau roman de physique.' Though its doctrines were recited

into the mid-eighteenth century the Cartesian system of science

proved sterile, and it may be doubted whether the Cartesian

philosophy of science ever produced a single useful thought, save

in the mind of its originator.1 The optimistic metaphysical belief

that what is clear and distinct must be true proved unfounded.

The deductive method, subjected to the destructive criticism of

the neo-Baconians of the Royal Society, was again convicted of

fostering works that were shallow, speculative and remote from

real things. Clearly when Descartes devoted himself to systematicshis status as a scientist diminished. But the importance of his

systematic works especially the Principles ofPhilosophy (1644), the

text-book of the Cartesian school for nearly a century must not

be underestimated, for in the mid-seventeenth century the intel-

lectual appeal of Descartes throughout France, Britain and north-

western Europe was immensely greater than that of Galileo, while

Bacon was almost unknown to continental scientists. The veryfact that Descartes wrote as a philosopher gave his scientific ideas

greater currency, and to many places where Aristotelean andhumanistic conventionality lingered untroubled, Cartesian notions

brought the first breath ofa new outlook, a fresrh vitality in natural

philosophy. Thus Oxford, because Descartes was read there, was

regarded about 1650 as being much in advance of Cambridge.His was undoubtedly the pre-eminent intellect in the swelling

movement, ebullient with ideas and discoveries, that made Paris

the scientific focus of Europe from about 1630 to 1670. Even

among those who cannot be enrolled with the expositors of Des-

cartes' science, there were many who, like Boyle or Newton,

though they learnt through the use of an empirical or Galilean

method to criticize his theories, had found in those same theories

their point of departure; indeed, the main activities in physical

1 It may be remarked that Descartes' metaphysic of scientific discovery, as

described in the Method, is essentially individualistic, i.e. it shows how each manmay learn to frame his own idea ofnature. But, just as those sects which claimedto be founded on the free interpretation of the Bible imposed the sternest disci-

pline in order to safeguard the interpretations of their founders, so the later

Cartesians instead ofgoing through this process ofdiscovery adhered rigidly to

the idea of nature developed by Descartes himself.


science for more than a generation after Descartes' death can be

interpreted, without gross distortion, as a commentary uponDescartes' works. And if the Principles of Philosophy proved ephe-meral compared with Newton's Mathematical Principles of Natural

Philosophy even the title suggests a reaction its influence in

leading later seventeenth-century science to entertain ideas of

mechanism, of the corpuscular structure of matter, of the im-

portance of "natural laws," was creative of further progress.

Perhaps it may justly be said that Descartes' successes in science

were due less to any peculiar merits in his method, than to his

native genius for investigation. There is one point, however, both

in the method and the texture of his thinking on scientific subjects

that deserves to be singled out. Descartes well understood the

importance, in any work of research, of scientific imagination, a

faculty with which he himself was so well endowed that he hardly

perceived its limitations when controlled by reason alone without

cautious experimentation. Bacon had recognized that imaginationor intuition might surmount an inconvenient obstruction; Galileo

also admitted that in demonstrative sciences a conclusion mightbe known before it could be proved:

Nor need you question but that Pythagoras a long time before he

found the demonstration for which he offered the Hecatomb, hadbeen certain, that the square of the side subtending the right angle in

a rectangle triangle, was equal to the square of the other two sides:

and the certainty ofthe conclusion conduced not a little to the investi-

gating of the demonstration. . . .*

In Descartes there is a more overt appreciation of the function

of directed imagination, playing on the problem in hand, in

formulating hypotheses to be tested by experiment or other means:

. . . the power of nature is so ample and vast . . . that I have hardlyobserved a single particular effect which I cannot at once recognize as

capable ofbeing deduced in many different ways from the principles, andthat my greatest difficulty usually is to discover in which of these

ways the effect is dependent upon them; for out of this difficulty I

cannot otherwise extricate myself than by again seeking certain

experiments, which may be such that their result is not the sameif it is in one of these ways that we must explain it, as it wouldbe if it were to be explained in another.2

1Dialogues (trans. T. Salusbury), p. 38.

* Discourse on Method, Part VI; my italics.


Here experiment is put forward, not as by Bacon to uncover the un-

known, or as by Galileo to confirm the known, but as a means of

eliminating all but one of the mechanisms suggested by imagina-tion as the explanation of a particular phenomenon. And as

Descartes correctly stated, the imagination is directed because it

is referred to certain known principles (or constructs), and further

because the mechanisms suggested must be susceptible in the

first place of deductive check, since science does not admit of

idle guessing. If Descartes had realized that even when only a

single hypothetical mechanism seems deductively feasible it

remains a hypothesis until confirmed by experiment, and if he

had applied this test more meticulously, his thought would have

been less liable to run into speculation. In any case the liberty to

frame hypotheses (in spite of Newton's famous dictum), with the

rigorous attention to the findings of experiment and observation

which Descartes himself neglected in his encyclopaedic survey of

nature, was to prove a creative factor in the accelerating progressof science.

The scientific method of the seventeenth century cannot be

traced to a single origin. It was not worked out logically by anyone philosopher, nor was it exemplified completely in any one

investigation. It may even be doubted whether there was any

procedure so conscious and definite that it can be described in

isolation from the context of ideas to which it was related. Theattitude to nature of the seventeenth-century scientists especially

their almost uniform tendency towards a mechanistic philosophywas not strictly part of their scientific method; but can this be

discussed except in connection with the idea of nature? In large

part the character of the method was determined by the mental

range of the men who applied it; hence Bacon's method bore

fewer fruits in his own hands because his conception of the facts

of nature was still Aristotelean. The influence of Descartes, too,

was so great because he produced a mechanistic world-system of

infinite scope (enriched with some genuine discoveries) which was

welcomed by his age, not because he outlined a remarkably clear

or satisfactory way of proceeding in scientific research. EvenGalileo's observations on method were probably less importantthan direct imitation of the kind of mathematical analysis heinitiated in mechanics. Over the broad area of scientific activity

the influence of content on form was more significant than the


reverse effect. Methods changed, because different questions were

asked, and a new view of what constitutes the most useful kind of

scientific knowledge began to prevail. Perhaps this is most effec-

tively revealed in the biological sciences, where the centurywitnessed a progressive change in the content of investigations

unaccompanied by conscious discussions of the methods to be

employed. Here there was no parallel to the criticism of the

methods of Aristotle and the scholastics in physics, though of

course the medieval neglect of the descriptive sciences was often

commented on adversely. The far-reaching inter-action between

the content and the techniques of science was also uncontrolled

by any very explicit conceptions of method. This interaction hada profound effect on the quality and extent of the information

available; but Bacon alone explicitly recognized the importanceof accurate fact-gathering in science. It seems most natural to

believe that in any effective step the method, the philosophy andthe discovery itself were carried along together in the subsequent

impact, for though there is nothing that can reasonably be called

a specific method of science to be found in the works of Harvey,or Kepler, or Gilbert, these men changed the character and formof future studies. Who, for instance, could ignore the challenge of

the phrase with which Gilbert opens his Preface to De Magnete:'Clearer proofs, in the discovery ofsecrets, and in the investigationof the hidden causes of things, being afforded by trustworthy ex-

periments and by demonstrated arguments, than by the probable

guesses and opinions of the ordinary professors of philosophy. . . .'

Yet the meaning and weight of experimental testimony was still

open to discussion a century later. A scientific approach to prob-lems must be the sum of its many aspects experimentation,mathematical analysis, quantitative accuracy, and so on varying

according to the nature of the problem; and this the seventeenth

century drew from many varied sources. Its implied implementa-tion in practice was more important than its explicit formulation,

with the somewhat curious result that scientific method, shapingitself to the needs of practising scientists and vindicated rather byresults than by preconceived logical rigour, has remained some-

thing ofan enigma to philosophers from Berkeley onwards. In the

long run the obstinate empiricism ofa Gilbert or the unpredictableintuition of a Faraday have successfully broken the rules of both

inductive and mathematical logic.

CHAPTER VII

THE ORGANIZATION OF SCIENTIFIC INQUIRY

E\CHphase of civilization tends to produce its own institutions

of learning. In the ancient empires science was attached to

the temples of religion; Greece saw Plato's Academy, the

Lycaeum founded by Aristotle, and the vast library of Alexandria;the middle ages created the common school and the university in

a structure of education which has not wholly vanished. Lastly,in the modern era, the learned society, with its international

affiliations and specialized journals, has profoundly influenced

the stratigraphy of research. Neither the learned society nor the

learned journal (the terms are convenient, if pompous) was

altogether the creation of the scientific revolution, but in both

cases the course of events was very much determined by the

necessities of the scientific movement, and scientific organizationwas taken as a model by those who worked in other fields of

knowledge. From the end of the seventeenth century the majorityof active men of science were members of some active scientific

group; publication in one of the ever more numerous journals

gradually became the recognized manner of announcing the

results of investigation; and the national scientific society was

accepted as the vehicle for the state's concern in scientific matters.

Although the Fellowship of the Royal Society, for example, wasmuch less indicative of intellectual distinction in the eighteenth

century than it has since become, as institutions the Royal Societyor the Academic Royale des Sciences enjoyed a prestige even

greater than that of the universities in humane studies. Indeed, the

evolution of modern science outside academic walls was the maincause of the lack of cohesion, and of the difficulty in the communi-cation of ideas, whose correction was one of the principal objectsof the founders of the scientific societies. In the unity of medieval

learning the scholar enjoyed communion with others of similar

interest in the university of which he was almost invariably a

member, and wherever his studies might lead him. The sixteenth

century saw the new phenomenon of scholars, literati and1 86

ORGANIZATION OF SCIENTIFIC INQUIRY 187

scientists whose interests were no longer embraced in the work of

the university, and who were also more uniformly distributed

throughout a highly cultivated society. The landed gentleman,the country physician or clergyman, the apothecary, the soldier

and the lawyer, played a new and important part in the advance-

ment of knowledge or the patronage of literature. Expecially in

northern Europe, where the universities were less numerous andmore conservative than those of Italy and France, intellectual

leadership passed to a class which was not merely outside the orbit

of the university, but was apt to regard academic learning as old-

fashioned and sterile.

Oxford and Cambridge are our laughter,Their learning is but pedantry:These Collegiates do assure us,

Aristotle's an ass to Epicurus.

wrote the "wit" who composed the Ballad ofGresham College about1 667.* From the first, the connection of the new scientific move-ment with practical arts rendered it in some degree independentof the universities. As the friends of the "new philosophy" became

increasingly critical of Aristotle and conventional education, theyfound their opponents the more firmly entrenched behind

academic walls; hence the innovators tended to seek a more con-

genial intellectual environment elsewhere. 2 Scientific knowledgewas no longer in the mid-seventeenth century limited to the

religious and medical classes, but was widely diffused through a

diversified and exuberant society. Many biographies relate the

feeling of confidence, the depth of intellectual satisfaction, the

release of a creative drive that was experienced by membersof the new class of laymen, educated and leisured, when they

passed from the confines of academic disputation to the methodsof experimental science.

Scientific discovery is (or was, until recent times) an act of the

individual, with of course a greater or less indebtedness to his in-

tellectual inheritance. So, equally, in the seventeenth century, was

the adoption of the novel scientific outlook, critical of orthodoxy,1 Gresham College, founded in 1 598 by the merchant-financier Sir Thomas

Gresham, was the first meeting-place of the Royal Society, whence the Fellows

were known as the "Gresham philosophers."8 In Europe, this was partly due to the control of education exercised by

certain religious orders, but everywhere the university was deeply committedto Aristotelean thought.


which can be seen almost as a conversion in many instances,

as when Galileo became an adherent of the Copernican system.

But since men naturally assemble to indulge a common taste, and

since wits are sharpened by contact, the groups of intellectuals

who collected in a tavern, a lecture-room, or about an enterprising

patron tended to assume a more formal character, to look for

recognition and privilege. The first of such groups to acquire an

organization and a history were products of Italian humanism.

Their interests were literary rather than scientific. About a centurylater the first national academy, the Academic Frangaise founded

by Richelieu in 1635, was also a literary institution: its main task

was the conservation of the purity of the French language. The

early literary societies met for discussion and criticism; their objectwas rather the extension of knowledge and the refinement of taste

than anything resembling research or analysis, and there was

nothing foreshadowing the modern presentation of papers. Thefirst scientific societies, which also originated in Italy, followed the

same pattern. Occasional meetings of groups of experimenters,like that which is supposed to have collected about William Gilbert

at his London house, or that centred about Giovanbattista Porta

in Naples (the so-called Accademia Secretorum Naturae) were

hardly societies at all.1 The first assembly emphatically of this

character was the Accademia dei Lincei in Rome, ofwhich Galileo

was a member, which lasted with one break through the first

thirty years of the seventeenth century. The Lincei2 rose to a

membership of thirty-two, and planned to set up branches every-

where, equipped with printing-presses, botanic gardens andlaboratories. The patron of the society was Duke Federigo Cesi,

a naturalist, and much of its activity was diverted to natural

history. One member, Francesco Stelluti, published the first

zoological studies made with the aid of the microscope. Two of

Galileo's early books were published by the Lincei, but the societydid not approve his later cosmological ideas.

The Accademia dei Lincei, like earlier literary societies, and somelater scientific groups, did not engage in any form of corporate

activity. The members followed their own investigations, whose

1Baptista Porta (d. 1615) was the author of Magi* Naturalis Libri IV (1558,

enlarged edn. 1589: Englished as Natural Magick, 1658), and a great exponentof esoteric experimentation.

1 So called, because the Lynx symbolized the clear-sightedness of science.


results they discussed at the meetings. However, the great Floren-

tine society of the mid-seventeenth century, the Accademia del

Cimento, followed the alternative plan, which had already beendescribed by Francis Bacon in the New Atlantis. The object of

Bacon's model organization was not merely to bring men together,but to set them to work in common on the tasks most importantfor science, so that it resembled a scientific institute more than a

modern scientific society. The vast realm of natural knowledge,he felt, was too vast for one man to tackle single-handed, while

concentration on a single problem or set of problems was likely

to produce a myopic picture of single trees, not a survey of the

forest. To the efforts of individual pioneers, as Sprat put it later

in speaking of the Royal Society, 'we prefer the joint Force of

many Men.' Other advantages of the Baconian plan were that,

as it ensured that due attention was always paid to each division

of science, so it made certain that none could be carried on in

complete isolation from the rest; and it also provided a means bywhich, it was hoped, "a quantity of necessary apparatus beyondthe means of a private purse could be gathered together.

In Bacon's view, the assembling of pure information, the

preliminary to the elucidation of natural truths, was such a

formidable task that it could only be tackled by a co-operativeendeavour. Otherwise science was likely to be for ever deluded

by theories enunciated on the basis of an insufficient mass of

digested fact.1 Later the Royal Society was for a short time to

embark on such a project of fact-collection. The Accademia del

Cimento, on the other hand, was not committed to this Baconian

conception of procedure in science. It concerned itself with the

experimental development of the scientific ideas of Galileo, and

of his two most successful pupils, Torricelli and Viviani, while the

nine members also pursued their own problems independently.One large fraction of their total activity was directed to the proofof the theorems on motion that Galileo had demonstrated mathe-

matically, and another to the study of the barometric vacuum

1 Thomas Sprat, in his History of the Royal Society (1667), echoed the then

typical opinion that in Bacon's writings were 'everywhere scattered the best

Arguments, that can be produced for the Defence of experimental Philosophy,and the best Directions, that are needful to promote it,' but he did not hesitate

to confess that Bacon's natural histories were far from accurate, because Baconseemed '

rather to take all that comes, than to choose, and to heap, rather thanto register

*

(1722 edn., pp. 35-6).

igo THE SCIENTIFIC REVOLUTION

discovered by Torricelli. Though the business of the society was

experiment, it was not by any means empirical experimentationalone. Reports of its work, which spread slowly throughoutscientific circles in Europe, did much to shape the course of

experimental science elsewhere, and created new confidence in

the Galilean experimental method. Part of the success of the

Accademia del Cimento in spite of its short duration often years

from 1657 to 1667 was due to the richness ofthe apparatus at its

command, for it made use of what was really the first physical

laboratory in Europe.1 The academy was founded by the Grand

Dukes Ferdinand II and Leopold of Florence, who used the

remaining wealth of the Medicis to buy the services of the finest

instrument-makers, to procure the most perfect lenses, and equiptheir colleagues with a most elaborate series of barometers,

thermometers, time-measuring devices and whatever else was

required for their work.

The book in which this was described the Saggi di Naturali

Esperienze (i667)2 was almost the first piece ofpure experimental

reporting in the history of science. Interpretation of the results

gained was limited strictly to the range of the evidence, andelaborate speculation was avoided. The experiments recorded

are various as well as numerous. Attempts were made to verify

Galileo's theory of projectiles, and the time-keeping properties of

the pendulum were studied without, however, leading to its

application to a mechanical clock, which was made by the Dutch

physicist Christiaan Huygens. Various forms of the thermometer,

hygrometer and barometer were tested, and the design of opticalinstruments improved. Experiments were made on the "radia-

tion" of cold from a lump of ice; on the thermal expansion of

many substances; on the incompressibility of water; on the force

of gunpowder; and on capillary attraction. The researches of

Torricelli and Pascal, showing that the observations formerly

explained by the statement that nature abhors a vacuum should

be attributed to atmospheric pressure, were confirmed. It was

proved that neither combustion nor respiration were possible in

a space exhausted of air, that magnetic attraction was transmitted

through it but not sound, and a rather unsuccessful attempt to

construct an air-pump was made. In this field of activity the

1 Many of the instruments are still preserved in Florence.1 Translated by Richard Waller as Essayes of Natural Experiments (1684).


Accademia was largely repeating work that had already been

done by Robert Boyle at Oxford, and described in his Pfysico-

Mechanical Treatise on the Spring of the Air(1 660) .

Naturally the benefits to be derived from closer co-operation

among those interested in the new scientific movement were not

perceived in Italy alone. In both England and France informal

groups had existed for many years before the Accademia del

Cimento was founded. The generation of Frenchmen which in-

cluded Descartes, Gassendi, Fermat, Desargues, Roberval, Pascal

and Mersenne (c. 163060) was particularly active, fertile both in

new ideas and new experiments. Paris was their centre, and there

was a continuous tradition of scientific gatherings which was

ultimately formalized in the Academic Royale des Sciences. Oneof the earliest groups was held together by the personality ofMarin

Mersenne, a Minim friar of the convent in the Place Royale,which was not only a meeting place at which important discussions

took place, but also the centre from which Mersenne conducted

his vast correspondence, maintaining communication between his

colleagues even more effectively than the actual gatherings. It is

a significant historical fact that, since the late sixteenth century,

transport facilities and postal organizations had much improved,

rendering possible regular and frequent exchanges of letters.1By

this means news of the latest developments could be spread more

rapidly: problems could be exposed for general consideration: andcriticism could be provoked and collated. In the mid-seventeenth

century a number of men occupied a prominent position, less

on account of their own intellectual capacities, than because of

their indefatigability as correspondents. Their function was to

be acquainted with everyone of importance in science, to gatherinformation and to re-distribute it to those of their friends whowere likely to be interested. Of these Fabri de Peiresc at Mont-

pellier was one, and Mersenne in Paris another. Later HenryOldenburg, first Secretary of the Royal Society, carried on the

same role, his talent as a "philosophical merchant" (as Robert

Boyle called him) greatly strengthening the bonds between

English and continental scientists. Even in the eighteenth centurythe private correspondence of a great public figure in science (like

Sir Joseph Banks) was still of international importance.1 Tycho Brahe was one of the first scientists to leave an important mass of

material of this kind, which has been edited by J. L. E. Dreyer.

iga THE SCIENTIFIC REVOLUTION

In London, as in Paris, informal groups preceded a formal

scientific society. These seem to have had a stronger commoninterest in the mathematical sciences than in moral and natural

philosophy, partly because geometry and astronomy were well

represented at Gresham College (the natural focus for scientific

pursuits in London), partly in continuation of the Elizabethan

tradition of developing the practical sciences (navigation, sur-

veying, cartography, etc.). While there was little evidence of

English concern for the ideas of Bacon, Gilbert and Harvey until

near the close of the first half of the seventeenth century, there

was considerable activity in the field where science and technology

overlap. Cornelius Drebbel, an ingenious engineer as well as an

experimenter of some repute, was acclaimed at the court of

James I,1 whose successor, besides patronizing Harvey's researches

in embryology, established an experimental workshop at Vaux-hall. Even the mathematician Napier of Merchistoun, inventor

of logarithms, in a fit of Protestant fervour invented a series of

terrible war-like devices, the plans for which he destroyed on his

death-bed. On the whole, the more important exponents of purescience in England at this early period, like Thomas Harriot

(d. 1621) and Jeremiah Horrocks (d. 1641), though by no means

isolated, had slender contact with the great scientific movementon the Continent. 2

Dilettanti, philosophers and literary men (suchas Thomas Hobbes, Sir Charles Cavendish and Sir William

Boswell) did more to make its literature known in England.

Indeed, the"grand tour" was a serious and necessary education,

as may be seen in the life of Robert Boyle.The history of the emergence of the Royal Society from these

groups has been told many times. It now seems probable that

there were two at least of these, whose members became the fathers

of real science in England; some men entered more than one

circle, but there was far from complete unity of ideas. In the

London of the Commonwealth and Protectorate men of antagon-istic religious and political persuasions could have very similar

1 Who paid a state visit to Tycho Brahe's observatory at Hveen, and received

the dedication of Kepler's Harmonices Mundi.2 Harriot was an inventive algebraist, and perhaps an independent dis-

coverer ofthe usefulness ofthe telescope in astronomy. He was closely connectedwith the Elizabethan explorers. Horrocks, in a very short life, proved himself atheoretical and practical astronomer of genius. He was an early student of

Kepler, with whom he had some correspondence.


scientific aspirations.1Something, at least, of Bacon's influence

may be detected in all; many wished to see some sort of specificallyscientific institution established, not a few were firmly convinced

that civilization could be powerfully advanced through scientific

knowledge. These last were particularly evident in the group that

Boyle called the "Invisible College" in 1646, who apparentlydevoted especial attention to agriculture, as well as to natural

philosophy and mechanics. The leading figure in this group wasSamuel Hartlib, a Polish refugee, a man of great learning andwide connections, an enthusiast for the union and defence of the

Protestant churches. Hartlib was a great advocate of the applica-tion of science to technology, but no scientist himself. His hopesbroken by the restoration of the monarchy, he appears to have

played no part in the foundation of the Royal Society that soon

followed. Another group included men of greater weight. As

John Wallis, the mathematician, recollected the events of 1645:

We did, by agreement, divers of us, meet weekly in London on a

certain day and hour, under a certain penalty, and a weekly contribu-

tion for the charge of experiments, ... of which number were Dr.

John Wilkins . . . Dr. Jonathan Goddard, Dr. George Ent, Dr.

Glisson, Dr. Merrett (Drs. in Physick), Mr. Samuel Foster . . . Mr.Theodore Haak . . . (who I think first suggested these meetings)and many others.

Haak was another German refugee, probably the most im-

portant of Mersenne's English correspondents. All those named

by Wallis (including himself), except Foster who died in 1652,were Original Fellows of the Royal Society. The group met in

term-time at Gresham College, and Wallis's list of topics in the

"New or Experimental Philosophy" which came up for discussion

recalls the subjects treated by the Accademia del Cimento:

Some were then but New Discoveries, and others not so generallyknown and embraced as now they are, with others appertaining to

1Thus, a circle close to the government included the poet Milton, Olden-

burg, probably John Pell (mathematician), Lady Ranelagh (Boyle's sister).

In touch with this was another group (Boyle's "Invisible College"?), whichincluded Hartlib, Boyle, Dury, Oldenburg, Plattes, Dymock, Petty, andevidently others. Then Wallis's group at Gresham College, also deeply com-mitted to the republican regime, was linked with the universities and the"Invisible College." Finally, the Royalists (Evelyn, Brouncker, Moray) seemto have maintained amicable relations with individuals (at least) in these

groups.


what hath been called the New Philosophy which from the times of

Galileo at Florence, and Sir Francis Bacon in England, hath been

much cultivated in Italy, France, Germany and other parts abroad,as well as with us in England.

It is interesting to note that the Copernican hypothesis was still

debated by these philosophers. About the year 1649 they were

divided, some moving to Oxford, where they formed the Oxford

Philosophical Society, which was joined by Boyle on his removal

there in 1653. In Oxford they were reinforced by some brilliant

students, among them Christopher Wren and Robert Hooke.

Thus there is considerable evidence that before the restoration

there existed an extensive ramification of personal connection

among at least thirty men, many of whom were prominent in

academic and public life, and that their common interest was in

mathematics and science, not in the promotion ofa religio-political

movement. The arch-royalist Evelyn could even visit Wilkins,

Cromwell's brother-in-law. Few were too deeply committed to the

republic to adjust themselves to the restoration of the monarchy,which provided an opportunity for effecting the formal organiza-tion long discussed among these amateurs. 1 Charles IPs dilettante

interest in science was well known, and his scientifically minded

courtiers, Sir Robert Moray 2 and Viscount Brouncker (later first

President of the Royal Society), were able to win his patronage.The Royal Society of London for the promotion of Natural Knowledge,

which received its first charter in 1662, was a wholly private

creation, very different from other major societies of the century.

Royalty gave patronage, but nothing more. The Fellows enjoyedneither privilege nor pension. They were granted no buildings or

funds. Therefore the Society remained, to the nineteenth century,

impoverished and inadequately housed. It has never possessed

1 In addition to the proposals of Bacon, Gomenius and Hartlib, plans weremade by Evelyn, Petty and Cowley. In the latter's plan sixteen resident pro-fessors were to teach 'all sorts of Natural, Experimental Philosophy, to consist

of the mathematics, mechanics, medicine, anatomy, chemistry, history of

animals, plants, minerals, elements, etc.; Agriculture, Art Military, Navigation,Gardening. The mysteries of all trades, and improvement of them; the Factureof all merchandises, all natural magic, or Divination; and briefly all thingscontained in the catalogues of natural histories annexed to my Lord Bacon's

Organon.' (A propositionfor the Advancement ofExperimental Philosophy, in Gowley'sWorks, 1680, pp. 43-51)-

1 Moray was a close friend of Huygens, and like Oldenburg he had attendedsessions of the Montmor academy in Paris.


laboratories, or other than honorary means of promoting research,

and was never able to implement the Baconian conception to

which many of the Founders were attached. For over a centuryand a half the qualifications for a Fellowship included wealth andinfluence as well as scientific merit, because without such supportthe Society would have collapsed. On the other hand, it had a

corresponding sovereignty over its actions. It was independent of

government, and though the specialist knowledge of the Fellows

was often placed at the service of the state (especially in the

eighteenth century), state officials guided neither its elections nor

its business. By contrast, in France the Academic Royale des

Sciences was the creation of the first minister, Colbert, who

arranged the appointments and suggested problems in accordance

with political interests. The members were pensionaries whenoccasion demanded, they became civil servants. That the Dutch

physicist Huygens, who retained his Fellowship of the Royal

Society throughout the Anglo-Dutch wars, found his position in

the Academic des Sciences inconsistent with Louis XIV's anti-

Dutch policy, and resigned from it, sufficiently indicates the

difference in character between the two institutions. And these in

turn correspond to the different social and constitutional structures

of the two states.

The middle-class intellectuals, who in England combined to

form their own clubs in which they met as equals, were in France,as in Italy, more dependent on the good offices of a patron. Thus,at the beginning of the seventeenth century, one of the groupsmost notable in Paris for literature and learning met regularlyat the residence of the historian de Thou. His patronage, which

included the use of his valuable library, was continued by his

relatives the brothers Dupuy to about 1662. Less exalted gather-

ings met at the Bureau fAdresse managed by the journalist

Renaudot. At these, as at the Cabinet of the Dupuys, literary and

political news was more eagerly awaited than discussion of

scientific topics. Mersenne's circle, however, confined its attention

almost entirely to mathematical and scientific affairs: it was he,

for example, who made the discoveries of Galileo and his pupils

known in France, who gave currency to the Cartesian system, and

publicized Pascal's problem on the cycloid.1 After Richelieu's

1i.e. the calculation of the area bounded by the curve and a straight line,

which proved to be three times the area of the generating circle.


foundation oftheAcademic Frangaise therewas some feeling amongthose who cultivated the sciences that encouragement ought to be

given to a similar non-literary institution. Among their numberwas Habert de Montmor, a man of great wealth who had offered

his patronage to both Descartes (who declined it) and Gassendi.

Not long after the death of Mersenne in 1648 weekly meetingswere taking place in his house, presided over by Gassendi. Their

discussions were not limited to science, and it was required onlythat those who took part should be 'curious about natural things,

medicine, mathematics, the liberal arts, and mechanics.' TheMontmor Academy, which gave itself a formal constitution in

1657, soon became a fashionable resort; at the meeting in 1658when Huygens' paper announcing his discovery of Saturn's ring

was read, there were present 'two Cordon Bleus . . . both Secre-

taries of State, several Abb& of the nobility, several Maitres des

Requetes, Conseilleurs du Parlement, Officers of the Chambredes Comptes, Doctors ofthe Sorbonne,' after which the amateurs,mathematicians and men of letters seem rather insignificant.

1

Science, even the most abstruse mathematics, had become respect-

able, and apparently interesting, even in the upper levels of

Parisian society. The new philosophies of Descartes and Gassendi

were victoriously allied against Aristoteleanism. But the course of

the Academy was not altogether smooth; the amateurs were

more ready to discuss the latest marvels in science than to workfor its advancement, and there were sharp clashes of personality.

Mazarin, who had shown far less concern for the intellectual

eminence of France than his master Richelieu, died in 1661 and

the supreme power was then committed to the young King,Louis XIV. There was thus the possibility of acquiring for science

the greatest of all patrons. Since the Royal Society had begun to

take shape in 1660 the Montmor Academy had followed its

fortunes with some envy, and had even to some extent modelled

its own proceedings upon the Royal Society's example. The links

between the two bodies were close, for Oldenburg correspondedwith several members of the Montmor Academy. Huygens andSorbiire (the Secretary of the Academy) were members of both

societies, and a number of the Parisians visited London.

The works of Boyle and other Englishmen were carefully

1 Saturn's ring had been seen in very distorted form by other astronomers,but Huygens first interpreted its nature correctly.


studied in Paris, where the usefulness of the empirical attitude was

gradually more highly esteemed. While the Royal Society had

grown from its own independent and varied origins, the Academicdes Sciences was certainly inspired by its success. In 1663 Sorbire

sent to Colbert, who was virtually Louis* Minister for Internal

Affairs, a copy of his memoir on a proposed reform ofthe Montmor

Academy. He regarded an experimental organization without

royal support as hopeless; soon afterwards the Academy did indeed

cease to exist, partly as a result of tension between the experi-mentalists and the philosophers. Meetings continued, however,at the house of Melchisedec Thevenot,

1 who also found the

expense of providing for experiments too great, and appealed to

Colbert. In a situation where co-operation between the Cartesians,

the Gassendists, the amateurs, the mathematicians and the experi-mentalists in a joint undertaking seemed increasingly impossible,the latter group turned to the monarchy. Their first scheme,

planned in an ample Baconian fashion, was severely pruned bythe minister. Ultimately the Academic des Sciences consisted of

two classes only, mathematicians (including astronomers and

physicists) and natural philosophers (including chemists, physi-

cians, anatomists, etc.), meeting jointly on Wednesdays and

Saturdays in two rooms assigned to their use in the Royal Library.

Appointments of the academicians were made during 1666, andsessions began at the end of that year.Most of the active members in the English groups preceding the

Royal Society became Fellows,2 but few of those associated with

earlier Parisian assemblies were received into the new Academic.

The systematic Cartesians were carefully excluded; on the other

hand, three foreigners, Huygens, Cassini and Roemer, were

among the most distinguished of Colbert's appointments. Thusthe Academic des Sciences was not strictly a continuation of anyprevious body, nor did it include the amateurs and dilettanti

admitted by the Royal Society. No rules or constitution exist

earlier than the reorganization effected by the Crown in 1699,but it is evident that as in England the precepts ofBacon were not

without weight. Huygens, especially, advocated the preparation1

(1620-92), traveller, linguist, author, student of many sciences, andinventor of the familiar spirit-level.

1 The few who did not seem to have retired into obscurity for political or

religious reasons, as Milton did; the election ofJohn Ray (1667) shows that the

Royal Society exercised considerable latitude in these respects.


of a complete Natural History, and the examination of newinventions was an important aspect of the Academic's work.

Having sketched a common programme, the pensionaries pro-ceeded to their experiments and discussions in concert. These

proceedings were strictly secret. As in London, the private

researches of the academicians gradually assumed a greater

significance than their co-operative undertakings. Yet the

Academic, thanks to its greater wealth, was able to attemptventures beyond the resources of the Royal Society. Two of them,the measure of a degree of a great circle about the earth, givingan accurate estimate of its diameter for the first time, and the

expedition to Tycho Brahe's observatory at Uraniborg, were

conducted by the astronomer Picard. A third, the expedition to

Cayenne (in which it was discovered that the length of the

pendulum beating seconds was less in southern than in northern

latitudes) had as its object the measurement of the earth's

distance from the sun by means of simultaneous observations on

Mars.1

Indeed, the study of astronomy by the members of the Acade-

mic was particularly successful. They developed the telescope of

very long focal length to its useful limit, the application of the

telescope to measuring instruments, and the use of the telescopemicrometer. Cassini's observations on Saturn, and Roemer's on

Jupiter (from which he correctly deduced the finite velocity of

light) won great fame. Some of these observations made at the

Paris Observatory provided important evidence for the system of

the universe which Newton was to substitute for that of Descartes.

They were made possible by royal generosity in equipping the

Observatory, built in 1666, which became an experimental insti-

tution as well as an astronomical observatory in the modern sense,

fitted with the finest instruments. For astronomy was the first of

the sciences to reach the stage where the results obtained bear a

definite ratio to the expenditure permitted. The Royal Society, bycontrast, was far less well provided for. It was not placed in control

of the Royal Observatory at Greenwich (founded in 1675), thoughit was granted some vague surveillance over it.

2 The equipment at

Greenwich, provided in the first instance by John Flamsteed, the

1 The result obtained was about 6 per cent, too small.* This somewhat anomalous situation provoked a serious conflict between

Flamsteed and the Society early in the eighteenth century.


Astronomer Royal, and his friends, was limited though good of its

kind. He himself was forced to take a country living for support,and could never afford proper assistance. His main work in de-

termining the positions ofthe stars was not available for more than

thirty years, but he supplied observations on the moon used byNewton in his gravitational theory. The credit for Flamsteed's

great achievement in reducing the errors of astronomical measure-

ment to a new low order, despite all the obstacles he had to over-

come, clearly attaches to himself alone. The Royal Society hadother observers ofnote, such as Robert Hooke and Edmond Halley

(Flamsteed's successor at Greenwich), but these had to do what

they could with their own resources. In fact the Society could offer,

at this period, no fit facilities for scientific work of any kind, apartfrom its library and museum.

Everywhere in Europe the formation of scientific societies illus-

trates a dual tendency, on the one hand towards the crystallization

of a specifically scientific organization out of informal groups

having broader and more superficial intellectual interests, and onthe other towards the preponderance ofthe experimentalists within

the organization. In Italy, France and England there was a transi-

tion from the discussion of natural-philosophic systems or hypo-theses to the verification and accumulation of fact; as the course

of the scientific revolution laid more emphasis on deeds than on

words, on the laboratory rather than the study, and as the prepara-tion of commentaries and criticisms of ancient texts gave place to

the writing of memoirs describing the results of systematic investi-

gation, so the characteristics of scientific organization changed

accordingly. In the first half of the seventeenth century the func-

tion of a scientific assembly had been to promote discussion anddissemination of the new idea of science, and to provide a forumin which, not merely before an audience of enthusiasts, but before

the broadest cross-section of educated and literate society, the

original thought of a Galileo or a Descartes could challenge con-

ventional opinions in science. Patrons like the Medici brothers, or

a newsgatherer like Mersenne, amassed the accumulative weightof innovation against the science of colleges and text-books. Theypresented the total case for the "new philosophy," in an intel-

lectual environment whose dogmatic traditions were already

disintegrating, to a new learned class freed from the sterner disci-

pline of the old professional scholar, ready to admire acuity of

aoo THE SCIENTIFIC REVOLUTION

wit, subtlety of reasoning and fertility of imagination more than

allegiance to orthodox" sound" views. If the "new philosophy"

was obstructed in the university, there was appeal through the

scientific assembly to the more tolerant, eager and wealthy in-

tellectual circles of court and capital. But the alliance between

modern science in its early stages and the whole turbulent current

of cultural development in the seventeenth century was inevitably

incomplete and of short duration. Important, creative scientific

work rapidly outdistanced the dilettante and virtuoso: rarely, for

example, does the name ofJohn Evelyn occur in the proceedingsof the Royal Society printed by Birch in his History. A man of

general culture could not see the point ofdetailed scientific labours,

for whereas he might enjoy a debate on Descartes' concept of the

animal as machine, he tended to find the naturalist grubbing in

ditches for insects' eggs merely comic. The exploitation of the

shift of intellectual perspectives, so fascinating in general outline,

inevnab!y sank to tedium and pedantry in the eyes of those who

sought entertainment and striking novelty. As a result, the Mont-mor Academy broke up, and the Royal Society failed in wide

appeal after its first fifteen years.

Consequently, in the second half of the seventeenth century the

role of the scientific society changed considerably. Having becomea thoroughly professional body, it served as a focus for the discus-

sion ofworks rather than ideas. Its aim was to develop the sciences,

rather than promote a "new philosophy." Opposition from Aris-

totelean university teachers, or the medical profession, was hardlyserious any longer. The scientific movement required countenance

less than means buildings, apparatus, money for the maintenance

of research, and methods for exchanging its results. It was found,for instance, that as scientific books became more truly technical,

more fully devoted to describing research (rather than useful text-

books or practical manuals), the publishing trade refused to handle

them unless large sums were laid down. Or again, while there wasan expanding commercial market for ordinary watches and clocks,

navigational instruments, and even telescopes and microscopes,financial encouragement alone would induce craftsmen to hazard

their profits in efforts to improve instruments for the advancementof science. In short, the task before a scientific society was less to

secure the scientific revolution, than to maintain its momentumand to reap its harvest. The founders of the Academic des


Sciences were perhaps the first to appeal to national interest in

this connection. 1 Earlier exponents of the utility of scientific dis-

covery had rather looked to the improvement of the condition of

mankind to a shift in the precarious balance between human

powers and the forces of nature. As Bacon had put it, the ambition

to exalt one's state was a degree less noble than the ambition ofthe

natural philosopher to elevate mankind. But in the proposals putforward by Leibniz, for example, to establish a scientific academyin Germany, there seems to be a clearer statement of the case for

investment in science as a national benefit. There the first scientific

academy, founded at Berlin in 1700, did not develop from the

efforts of earlier groups of amateurs. 2 The capital of Brandenburg-Prussia was indeed far removed from the main centres of culture

in Germany, its university not being founded until more than

a century later, but Leibniz had in the Elector (later King)Frederick I a patron willing to realize his long-matured plans. These

had always aimed at furthering the interests of the German nation

and raising its technological standards through the encourage-ment of the vernacular language and the reform of education in a

practical direction. To attain these objects a national academywhich should concern itself with practical applications as well as

with the pure sciences was the first necessity. In Leibniz* view

Germany had once enjoyed pre-eminence in useful arts, especiallyin mining and chemistry,

3 but also in horology, hydraulic engin-

eering, goldsmith's work, turnery, forging etc. Astronomy wasrestored by the Germans, and the

" Nieder-Deutschen"

(Nether-

landers) had invented the telescope and mastered navigation.The only remedy for the subsequent deterioration was the generous

encouragement of science, which Leibniz coupled with the en-

forcement of a strictly mercantilist economic policy, by which the1 'Sans exclure de son programme deludes les sciences pures et spe*cu-

latives, Colbert essaie de 1'orienter vers les sciences applique*es a 1'industrie et

aux arts." P. Boissonade: Colbert (Paris, 1932), p. 28.2 There were already active scientific groups in Germany in the late

seventeenth century such as the Collegium Nature Curiosorum, founded byLorentz Bausch in 1652 and dealing with the medical sciences, and the

Collegium Curiosum sive Experimental*, founded by Christopher Sturm of the

University of Altdorf in 1672 and dealing with physical sciences. Neither wasa national academy of science in any sense.

8 'Denn weil keine Nation der Teutschen in Bergwcrgssachen gleichcnKonnen, is auch Kein Wunder, dass Teutschland die Mutter der Chimiegewesen.' L. A. Foucher de Careil: OSuvres de Leibnitz (Paris, 1859-75),vol. VII, pp. 64-74.


state should become self-sufficient.1 As he put it in a letter to

Prince Eugene,discussingtheproposed scientific academy inVienna :

Pour perfectionner les arts, les manufactures, Tagriculture, les deux

esp&ces d'architecture [i.e. civil and military], les descriptions choro-

graphiques des pays, le travail de mini&res, item pour employer les

pauvres au travail, pour encourager les inventeurs et les entre-

preneurs, enfin pour tout ce qui entre dans Vuconomique ou mtcanique de

I'etat civil et militaireyil faudrait des observatoires, laboratoires, jardins

de simples, menageries d'animaux, cabinets de raretez naturelles et

artificielles, une histoire physico-me*dicinale de toutes les annees sur

des relations et observations que tous medecins salaries seraient

obligez de fournir.2

Leibniz, historian, mathematician, philosopher, diplomatist andconfidential adviser of princes, in his dual devotion to science and

Germany saw the scientific academy as a necessary instrument of

the modern state, through which science could be made to playits due part in social and economic policy. He had little patiencewith those who '

considrent les sciences non pas comme une

chose tr&s importante pour le bien des hommes, mais comme unamusement ou jeu,' and criticized the Academic des Sciences

for this reason.3 Science as a factor in creating national prestige,

its role in war and in the commercial rivalry of states, were

appreciated in England and France as well as in Germany; but

no one who could claim high rank as a philosopher and scientist

announced the importance of scientific organization to jealousstatesmen more clearly than Leibniz.

Thus, one alleviation of the obstructions to scientific progresswas sought through the conversion of Bacon's appeal to the inter-

ests of humanity into an appeal to the interests of the state.4 One1 On mercantilism, cf. E. Hecksher: Mercantilism (London, 1935). The

Berlin Academy was intimately linked with Leibniz* typically mercantilist

project for the establishment of a silk industry in Brandenburg. (Foucher de

Gareil, loc. cit. 9 pp. 280 et seq.)* Ibid,

y p. 317, italics inserted.8 Letter to Tschirnhaus, January 1694 (C. I. Gerhardt, Mathematische

Schriften, in Gesammeltc Werke hrsg. von G. H. Pertz, vol. IV, p. 519).4 In the later seventeenth century gunpowder was still quoted as one of the

great discoveries of the modern age. War was accepted by scientists, as by all

men, as an inevitable human evil, and the development of the war-like potentialof the state did not provoke moral condemnation, perhaps because this genera-tion experienced warfare which was more technically efficient than that of

previous generations, but which the lessening of religious fanaticism hadrendered less horribly destructive. Many scientists, however, commented that

it was more noble to advance the arts of life than those of death.


other must be briefly treated. The Royal Society approved a stepwhich was calculated to increase its support in a rather different

way, by the publication of its Philosophical Transactions, begun in

1665. Partly a profit-seeking venture on the part of the Secretary-

editor, Henry Oldenburg, the Transactions were also intended to

attract the "curiosi" and "virtuosi" to the work of the Royal

Society, and to stimulate the submission of original reports. The

publication consisted of discourses read by Fellows at meetingsof the Society, of letters on scientific subjects (translated, if neces-

sary, and printed more or less verbatim), both from Britain and

abroad, most of which also had been read at meetings, and of

book-reviews. The modern scientific "paper," of which the first

examples appear in the Philosophical Transactions, has in fact a

double origin. One of its ancestors exists in the interchange of

scientific correspondence discussing original work, which may be

traced back to the late sixteenth century. Very many of Olden-

burg's articles were letters with hardly more than the "Dear Sir"

and "your obedient servant" deleted: but they were letters in-

tended for publication. The other ancestor was the formal essayor discourse read to scientific groups from the early seventeenth

century onwards. At the time, this form of presentation requiredthe development of a new art of composition, for no suitable liter-

ary or academic models existed and its perfection, leading to the

complex machinery for scientific reporting existing today, is an

event of historical importance. At the end of the century, however,the learned journal was still far from being the accepted meansfor the announcing of discoveries. Huygens, for instance, thoughhe stated his results in bald (or even enciphered) language to

the societies of London and Paris, published them completely

only in full treatises which sometimes appeared many yearslater.

Nevertheless, the Philosophical Transactions was immensely suc-

cessful. Latin translations were produced at Amsterdam, andthe Academic des Sciences prepared its own French version.

Though Antoni van Leeuwenhoek, the great microscopist, never

visited London and knew no language other than his native Dutch,he sent the accounts of his astonishing discoveries for publicationin English in the Transactions. Oldenburg had created a new field

of literature, which was rapidly extended; for if the Transactions

was not the first journal to appear in regular numbers, it was the


first to print original communications. Its predecessor by two

months, the Journal des Sfavans, surveyed the whole field of

learning, devoted much space to summaries of books, and merely

reported the business of the scientific societies. The series of

original Mtmoires of the Academic des Sciences was begun onlyafter the reorganization of 1699. Many other reviews, of which

the most famous was Bayle's Nouvelles de la republique des lettres

(1684) followed the broad pattern of the Journal; a few others (the

Miscellanea published by the Collegium nature curiosorum from 1670,and the Acta Eruditorum founded by Leibniz in 1682, the former

restricted to the medical sciences and the latter embracing manyaspects of learning) printed communications, but none was so

purely descriptive in its content as the Philosophical Transactions.

While the reviews enjoyed a steady repute among intelligent

readers, and gave a superficial picture of the total scientific

activity in Europe, private communication in correspondence,and the frequent exchange of their respective publications, was

for the leading figures far more important.

From the preceding account, it will be clear that during the

mid-seventeenth century there was a tendency for all effective

scientific activity to be focused upon some society or group. In

the small area of England a single organization embraced every-

one, but in France and Germany, both before and after the

foundation of national academies, less magnificent societies

flourished, as they did also in the Italian and other small states.

Each of these had its own character and major preoccupations.

Naturally also each proclaimed, with varying degrees of emphasis,the principal tenets of the scientific revolution. Strategic concepts,like that of natural law, gradually gained a universal validity; the

practical benefits to be expected from the cultivation of natural

science were canvassed in all parts of Europe; Aristotelean

philosophy was everywhere condemned, and the virtues of

mathematical analysis everywhere exalted; nearly all the societies

embarked on elaborate programmes of experiments. The societies

differed in character, and individual members of the same society

differed in their opinions; in France Descartes, and in EnglandBacon, were regarded as peculiarly magisterial figures, but it is

commonplace to find members of different societies working onthe same or allied problems in similar ways, or to discover the


reaction of some discussion in Gresham College upon the work of

the Parisian academy, and vice versa. Only to a strictly limited

degree did local or personal traditions bar the complete amalga-mation of the new scientific spirit.

Perhaps this may best be illustrated in the development of a

mechanistic view of nature during the seventeenth century. This

proceeded at three different levels. In the first place, a mechanistic

theory of the universe was fully described by Descartes in 1644

(in the Principles of Philosophy) ,to be supplanted by the far more

perfect theory of Newton's Principia (I687).1Spheres and intelli-

gences were finally banished, and the secrets of the heavenlymotions were traced to the properties of matter and the rule of

laws of nature. Secondly, in biology, the theory of the organismas a machine was taken up by the Cartesian school, and exercised

a wide influence; this theory, of course, was the product of a shift

in philosophical outlook. Newtonian mechanism could be shownto satisfy all the minutiae of evidence; biological mechanism wasa profound hypothesis, but no demonstration of it in physiologicalterms as yet existed, or was possible. In the third place, mechanistic

views in relation to physics and chemistry fall into an intermediate

category. They could not be demonstrated completely, but theycould be applied successfully in a number of particular instances.

They were certainly philosophical in origin, and not deductions

from definable experimental investigations, but they were

applicable in a wide area of experimental research.

At each of these levels, the attitude of the mechanistic scientist

to the complexity of nature enabled him to cope with different

fundamental problems. Pure and celestial mechanics, the most

highly mathematical branches of science, treated of the nature

offerees and motion. Mechanistic biology gave a new interpreta-

tion of the nature of life, of growth and of sensation. In relation to

physics and chemistry, the problem to which the scientist soughtan answer was the nature and constitution of matter, in so far as

these sciences dealt with the properties, changes and transforma-

tions of inorganic substance. The distinctions between the three

states of matter; differences in density and mass, hardness and

1 The Principia exposes, of course, no mechanistic theory of the nature orcause of gravitational forces. Newton's conjectures, on various occasions, makeit plain that he leaned strongly towards some form of mechanistic interpreta-tion. See below, pp. 272-3.


brittleness; the nature of magnetism, electricity, gravity and heat;

hypotheses oflight and colour, all seemed to require interpretationin the light ofsome general theory ofwhat matter is, which would

account for the variations in observed properties between different

kinds of material substance. Similarly the philosophical chemist,

studying solution, volatilization, fusion, and the analysis and

synthesis of substances effecting striking qualitative changes in

macroscopic properties, necessarily tried to form some picture of

what was happening to the very nature of the materials in his

vessels. Starting from the axiom that matter is neither created nor

destroyed, what internal modification was implied by a changein observable qualities?

During the sixteenth and seventeenth centuries there was, as

might be expected, a sharp reaction against the answers which

Aristotle had furnished to this type of question. In the period of

the foundation of the Royal Society and the Academic des

Sciences various versions of a mechanistic, particulate theory of

matter were widely entertained. As in other matters, there was a

tendency for the scientific revolution to revert to a Greek view of

nature older than Aristotle's. Medieval philosophers had, very

largely, respected Aristotle's condemnation of atomistic doctrines,

but the scholars of the renaissance and the scientists of the seven-

teenth century, with the full text of Lucretius' exposition of Greek

atomism in their hands,1

preferred its use of the concepts of

structure and physical texture in matter to Aristotle's theory of

forms and qualities. The Greek atomists had explained the com-

plexities of substances without making any assumptions of a

non-material nature; indeed, if Lucretius was right in his declara-

tion that the only realities are atoms and the vacuum in which

they move, qualities were mere illusion, the perceptual registration

of physical reality.2 This was a virtue of the "mechanical" or

"corpuscular" philosophy particularly attractive to Galileo, for

example, who sought to penetrate by means of the process of1 There were about thirty editions ofDe Natwra Rerum (editio princeps, Brescia,

1473) before 1600. There was a French translation in 1677, and an Englishin 1683.

* By contrast, in the older philosophy, forms and qualities were real, existingentities. If it was said that snow had the "form of whiteness,'* this did notdescribe the snow, but explained its optical properties. Similarly for the

alchemists the "form ofgold" was something that could be separated from the

"substance" of gold and transferred to the "substance" of another metal,

e.g. lead deprived of its own distinctive "form."


abstraction from the evidence of sensation to the basic reality of

nature.

Before Descartes' influence became significant a number of

writers had expounded or commented on ancient particulate

theories, drawing on the texts of Democritus, Epicurus, Lucretius

and Hero of Alexandria. The earlier ones treated the atomistic

doctrine purely as a theory of matter, which they freely combinedwith Aristotelean physics. Pierre Gassendi, from about 1625, was

the first writer to attempt to develop a completely mechanistic

physics founded on Epicurus and rejecting Aristotle, but his

success was hardly greater than that of Lucretius, whom, exceptin matters touching on religion, Gassendi very closely followed.

Physical properties were simply traced to the imagined size and

shape of the component particles. In Galileo and Bacon, on the

other hand (as already mentioned), are found the beginnings of

a true kinetic theory, especially in relation to heat. As Isaac

Beeckman stated it, 'all properties arise from [the] motion,

shape, and size [of the fundamental particles], so that each of

these three things must be considered.'1 For both Bacon andGalileo an important aspect of the "new philosophy" was its

endeavour to establish, through experimental study, a theory of

particulate mechanisms to replace the doctrines of forms and

qualities, yet neither of them were atomists in a narrow sense.

Bacon, indeed, wrote that the proper method for the discovery of'

the form or true difference of a given nature, or the nature to

which nature is owing, or source from which it emanates' wouldnot lead to 'atoms, which takes for granted the vacuum, and

immutability of matter (neither of which hypotheses is correct),

but to the real particles such as we discover them to be.' 2 In

short, there is ample evidence that in the early seventeenth centurythe conception ofmatter as consisting of particles, whose aggregate

might be a solid, a liquid, an air or a vapour, was commonplaceand generally acceptable and that the properties of the aggregatewere attributed to the nature and motions of the particles.

In considering the development, extension and diversification

of this generalized concept in the second half of the century, three

traditions may be distinguished. The first is that of the strict

1Journal Unu par Isaac Beeckman d* 1604 a 1634, *& Cornelia de Waard (La

Hayc, 1939-45), vol. I, p. 216 (1618).1 Novum Organum, Bk. II, Aphorisms i, viii.

ao8 THE SCIENTIFIC REVOLUTION

atomists, adhering firmly to the indivisibility of the ultimate

particle and the absolute reality of the vacuum between atoms.

They were the followers of Gassendi. Next, Cartesian scientists

continued the peculiar corpuscularian doctrine of Descartes,which

admitted the infinite divisibility ofmatter, and denied the vacuum.

Finally, the experimentalists refused to commit themselves to any

precise body of philosophic preconceptions. They learnt from both

Gassendi and Descartes: the form of their particulate theory was

closer perhaps to that of Gassendi, but in its application to physicsit borrowed much from Descartes' concrete imagination. This

experimentalist tradition in corpuscularian physics grew most

rapidly in England, and was especially fostered by the works of

Robert Boyle. Never a dogmatic system, it was a late developmentwhich played an important part in the relations between the

French and English scientific societies. It was, in fact, a major

product of the impact of French scientific ideas upon Englishmenabout the middle of the century an impact which conditioned

the nature of the scientific achievement of the Hooke-Boyle-Newton generation.

Starting from the assumptions that in nature there are no occult

forces, like gravity or magnetism, and that the universe is continu-

ously and completely filled with matter, Descartes developed in

the Principles of Philosophy (1644) an extraordinarily elaborate

mechanistic and corpuscularian" model' 'of the physical universe.

His particles, of which there were three species, were not atoms,because he imagined them as divisible, though in nature not

normally divided. The first element was a fine dust, of irregular

particles so that it could fill completely the interstices between the

larger particles. The second element (matiere subtile or aether) con-

sisted of rather coarser spherical particles, apt for motion, and the

third element of still more coarse, irregular and sluggish particles.

These three elements corresponded roughly to the Fire, Air andEarth of Aristotle, and as they were composed of the same matter,the elements could be transformed one into another. This was

regarded by the Cartesians as no arbitrary hypothesis, but as a

truth (according to Rohault) 'necessarily following] from the

Motion and Division of the Parts of Matter which Experience

obliges us to acknowledge in the Universe. So that the Three Ele-

ments which I have established, ought not to be looked upon as

imaginary Things, but on the contrary, as they are very easy to


conceive, and we see a necessity of their Existence, we cannot

reasonably lay aside the Use of them, in explaining Effects purelyMaterial. 51 The nature of a substance was mainly determined byits content of third element, its properties by the second. Since

Descartes denied that the third-element particles had intrinsic

weight or attraction, hardness (the cohesion of these particles) was

attributed to their remaining at rest together, fluidity to their

relative motion; but this motion also was not intrinsic but im-

parted by the first and second elements. Thus in solution the

grosser particles of the solvent by their agitation dislodged those

of the dissolved material; if however the particles of the solvent

were too light, or the pores of the solid material too small to admit

them, the latter would not dissolve. When the pores between the

third-element particles were large enough to admit a large quan-

tity of the second element, the substance was an "elastic fluid"

(gas), whose tendency to expand was caused by the very free and

rapid motion of the second-element particles. Flame itself con-

sisted of matter in its most subtle form and under most violent

agitation, and was therefore the most effective dissolvent of other

bodies, while the sensation of heat increased with the degree of

motion in the particles of the heated body. Rohault notes that,

when filed, copper grows less hot than iron because, copper beingthe softer metal, its particles do not require such violent agitationto separate them as do those of iron. 2 The greater motion associ-

ated with heat was also the cause of thermal expansion. Lightwas thought to be 'a certain Motion of the Parts of luminous Bodies

whereby they are capable of pushing every Way the subtil Matter

[second element] which fills the Pores of transparent Bodies,' and

secondary illumination was attributed to the tendency of this

matter to recede from the luminous body in a straight line. Trans-

parent bodies had straight pores through which the matiere subtile

could pass, opaque bodies blocked or twisted pores. If this exertion

of pressure by the luminous body were confined or resisted, it

would grow hot. Refraction and reflection of this pressure (or

1John Clarke (trans.) : Rohault's System of Natural Philosophy Illustrated with

Dr. Samuel Clarke's Notes Taken mostly out ofSir Isaac Newton's Philosophy (London,1723), vol. I, pp. 1 15-17. Jacques Rohault (1620-72) was the greatest of all

expositors of Cartesian physics; his TrmU de Physique appeared first in 1671.Clarke's Notes strongly oppose Newtonian corpuscularian ideas to those ofDescartes.

Ibid., p. 156.


rather pulse) which is Light were explained by analogy with the

bouncing of elastic balls. 1 In dealing with magnetism Cartesians

were careful to emphasize that*

though we may imagine that

there are some Particular Sorts of Motion which may very well

be explained by Attraction; yet this is only because we carelessly

ascribe that to Attraction, which is really done by Impulse9

; as

when it is said a horse draws a cart, whereas it really pushes it bypressing on the collar. 2

Magnetic effects were actually caused bystreams of screw-like particles, entering each Pole of the earth and

passing from Pole to Pole over its surface, which passed throughnut-like pores in lode-stone, iron and steel, and thus were capableof exerting pressures on these magnetic materials.

By theorizing in this way on the different motions of the three

species of matter the Cartesian physicists tried to account for all

the phenomena of physics as known in the second half of the

seventeenth century. They had some striking contemporary dis-

coveries on their side: for instance, the discovery that the rising

of water in pumps and analogous effects were not due to horror

vacui or to attraction, but simply to the mechanical pressure of the

atmosphere. They also explained gravitation mechanically as a

result ofpressure, and extended their corpuscular ideas to chemical

reactions. The idea of particulate matter-in-motion was therefore

the very foundation of Cartesian science, the basis of a homo-

geneous system of explanation. The fact that (in Rohault's words)'the few Suppositions which I have made . . . are nothing com-

pared with the great Number of Properties, which I am going to

deduce from them, and which are exactly confirmed by Experi-ence* was a strong reason for believing 'that That which at first

looks like a Conjecture will be received for a very certain andmanifest Truth.*3 As expounded by Descartes and his successors

this "mechanical philosophy" was illustrated by many qualitative

experiments; but these could hardly be said to prove the Cartesian

system, which always remained, in addition, entirely non-

mathematical.

Nevertheless, Cartesian science had a great influence upon the

Fellows of the Royal Society. Just as, in the past, Aristotle's teach-

ing was the inevitable starting-point for scientific thought, so they

1Clarke, op. cit., vol. I, pp. 201 et seq.

Ibid., vol. II, p. 166.*

Ibid., vol. I, p. 203; vol. II, p. 169.


often found their point of departure in Descartes. For Boyle,

indeed, 'the Atomical and Cartesian hypotheses, though theydiffered in some material points from one another, yet in opposi-tion to the Peripatetic and other vulgar doctrines they might be

looked upon as one philosophy.' While older philosophers had

given but superficial accounts of natural phenomena, relying onan incomprehensible theory of forms and qualities, the moderns

agreed in explaining 'the same phenomena by little bodies

variously figured and moved.' The differences between the

modern schools were rather metaphysical than physical, and did

not greatly affect the study of the world as it actually is.1Appar-

ently the English experimentalists who formed the Royal Society

already held eclectic opinions: 'they found some reason to sus-

pect/ wrote Hooke in his Preface to Micrographia (1665), 'that

those effects of Bodies which have been commonly attributed to

Qualities, and those confess'd to be occult, are perform'd by the

small machines of Nature.' Over this wide and in many waysstrategic area of scientific thinking the English and French socie-

ties spoke the same language and shared a common inheritance

of ideas. The differences between Cartesians and Gassendists werefound in both alike, and the appeal to a particulate theory of

matter was as common in England as in France.

Though the experimenters of Gresham College were far from

being pure empiricists, in giving high praise to Descartes' system

they did not forget their other allegiances to Bacon, Galileo andGilbert. Few were dogmatic or literal followers of Descartes.

Accepting the general form of the "mechanical philosophy," theymeasured Cartesian science rigorously by the experimental test.

Hooke challenged its theory of light and colours, Boyle its theoryof elastic fluids, and Newton its cosmology. Yet even the last of

these suggested a space-filling aether, and questioned whether the

most subtle effects ofnature were not obtained by purely mechani-

cal means. The very titles of Boyle's works indicate the tendencyof his thought: The Excellence and Grounds of the Mechanical Philo-

sophy; The Origin ofForms and Qualities, an introduction to the same;The Mechanical Origin of Volatility and Fixedness; The Mechanical

Production of Electricity; The Mechanical Origin ofHeat and Cold; with

many more in a similar vein. And during the greater part of his

1 Certain Physiological Essays (publ. 1661 but written some yean earlier).

Works, ed. T. Birch (London, 1772), vol. I, p. 355.


scientific career, from about 1655 at least, he devoted himself to

trying 'whether I could, by the help of the corpuscular philo-

sophy . . . associated with chymical experiments, explicate some

particular subjects more intelligibly, than they are wont to be

accounted for, either by the schools or [by] the chymists.'1 In his

Excellence and Grounds of the Mechanical Philosophy Boyle defined his

position exactly:

God, indeed, gave motion to matter; ... he so guided the motions

of the various parts of it, as to contrive them into the world he de-

signed to compose; and established those rules of motion, and that

order amongst things corporeal, which we call the laws of nature.

Thus, the universe being once fram'd by God, and the laws ofmotion

settled, and all upheld by his perpetual concourse, and general provi-

dence; the [mechanical] philosophy teaches, that the phenomena of

the world, are physically produced by the mechanical properties of

the parts of matter, and that they operate upon one another accord-

ing to mechanical laws. 2

Here Boyle appeals for justification of his natural philosophy to

the divine plan of creation (thus withdrawing himself from the

atheistic connotations of Epicureanism, and from the evolutionary

suggestions of Descartes) ; seeing the world as a machine indeed,

but a machine whose complex processes are continually supervised

by a divine providence. Though his world-picture transcended

the evidence of experimental science, Boyle was convinced that

the details of the mechanism of nature could only be revealed

through experimental study. It might even be more useful not to

attempt at this stage to relate observed physical phenomena to

the 'primitive and catholick affections of matter, namely bulk,

shape, and motion,' but rather to intermediate physical proper-ties such as hardness, temperature and so forth. Therefore he did

not hesitate to doubt the necessity of Descartes' rectitude. Hedoubted whether the air in an exhausted vessel was really replaced

by a matiere subtile',of whose existence he was generally sceptical.

3

He attributed the elasticity of air to the springiness of its particles.

He was much more vague in his pronouncements on the basic

1 Some Specimens of an Attempt to make Chymical Experiments useful to illustrate

the Notions of the Corpuscular Philosophy. Works, 1772, vol. I, p. 356.1 Peter Shaw: Works ofBoyle abridged (London, 1725), vol. I, p. 187.8 The matiere subtile (or aether) in an exhausted space was used by Cartesians

generally to explain the transmission of light, and by Huygens to account for

effects of surface tension in vacua.


structure ofmatter than Descartes, indicating only that he thoughtit composed of fundamental particles, and larger aggregates of

these, the real corpuscles. The particulate theory was related byDescartes to the Aristotelean four-element doctrine, but not byBoyle. He was sceptical also ofthe Cartesian interpretation ofmag-netism and electricity. He carried through a far more thorough-

going mechanistic attack on the doctrine of "forms" than the

Cartesians. Moreover, while the Cartesians sought to illustrate a

theory of nature by experiments, Boyle sought to interpret his

experimental researches in the light of the corpuscular philosophy.The distinction is perhaps subtle, but it is real. For besides his

sense of the ultimate truth of a mechanistic view of nature, Boylewas also imbued with Bacon's conception of the scientist's com-

piling histories of nature, and promoting the progress of material

civilization. In the last resort his devotion to the corpuscular

philosophy seems to have been grounded less on an opinion that

it was a key to the final understanding of nature, than on the con-

viction that it provided a broad framework of ideas within whichscientific research could most rapidly progress towards this final

understanding.If Boyle presented the corpuscular philosophy more elaborately

than any other Englishman, the influence of Newton on non-

Cartesian particulate theories of matter was perhaps ofeven longerduration. His successors did not hesitate to read the Queries ap-

pended to Newton's Opticks (1704) as though they were state-

ments of his considered opinions. Newton's views on the structure

of matter are indeed shadowy. The famous Hypotheses non Jingo is

not to be taken too literally, but he certainly would not have ac-

cepted Rohault's easy dictum that a conjecture agreeing with the

properties of things may be taken as very probable. The questionswhich Newton felt impelled to ask, and the answers to them at

which he hinted, were indeed only made public because Newtonknew that his scientific career was over. The experiments needed

to gain further insight into these problems he would never per-form. Yet Newton had confidence enough in his opinions to

declare:

It seems probable to me, that God in the Beginning form'd matter in

solid, massy, hard, inpenetrable, movable Particles, ofsuch Sizes and

Figures, and with such other Properties, and in such proportion to

Space, as most conduced to the End for which he form'd them. . . .


These, then, were true atoms; endowed with 'a Vis inertia,

accompanied with such passive Laws ofMotion as naturally result

from that Force,' and with 'certain active Principles, such as is

that of Gravity, and that which causes Fermentation, and the

Cohesion of Bodies.' Such principles were not occult qualities,

like those of the Aristoteleans, because they were made precisely

known by experiment; only the causes of them were hidden. * Ofthe particles Newton asked, have they not also

*

certain Powers,

Virtues, or Forces, by which they act at a distance, not only uponthe Rays of Light for reflecting, refracting, and inflecting them,but also upon one another for producing a great Part of the

Phenomena of Nature?'

He confessed that these "Virtues" might be veritably performed

by impulse, but their cause was only to be unfolded through studyof the "Laws and Properties of the Attraction." 2 To attraction

between particles he attributed cohesion and the strength of

macroscopic bodies, the force being very strong in immediate

contact, but reaching 'not far from the Particles with any sensible

Effect.' Thus the particles were compounded (as Boyle had sug-

gested) into corpuscles of weaker attractive force, and so success-

ively into the largest aggregates 'on which the Operations in

Chymistry, and the Colours of Natural Bodies depend, and which

by cohering compose Bodies of a sensible Magnitude.'3 Newton

was the first to point out that in any apparently solid body the

volume of matter is small compared with the volume of spacebetween the particles, and to think of each particle as surrounded

by a field of force. Again, he asked:

Is not . . . Heat . . . conveyed through the vacuum by the vibra-

tions of a much subtiler Medium than Air, which after the Air wasdrawn out remained in the Vacuum? And is not this Medium the

same with that Medium by which Light is refracted and reflected. . . .

And is not this Medium exceedingly more rare and subtile than the

Air, and exceedingly more elastick and active? And doth it not

readily pervade all Bodies? And is it not (by its elastic force) expandedthrough all the Heavens?

But this Newtonian aether was very different from the Cartesian.

As the cause of gravity Newton imagined it as being more rare

1 Sir Isaac Newton: Opticks (with Introduction by Sir E. T. Whittakcr,London, 1931), pp. 400-1.

2Ibid., pp. 375-6. Ibid., pp. 389, 394.


in solid bodies than in free space; where it must be of the order

one million times less dense than air, but more elastic in the same

proportion.1 With regard to the theory of light, it seems futile to

try to harmonize the different notions referred to in the Queries.

Newton's views involved a compromise between the"undulatory

"

and "corpuscular" theories, and in different passages he seems,as it were, to be operating at different depths of thought. But

whether he spoke of light as a vibration in the aether, or as a

stream of particles issuing from the luminous body, he was at

once mechanistic and anti-Cartesian. Similarly he gave a purelymechanical account of the physiological nature of vision.

The Queries are highly suggestive. The reader half-glimpses

entrancing vistas of the territory to be conquered by the "me-chanical philosophy." In the early eighteenth century a numberof rather unfruitful attempts to take Newton's ideas further were

made, especially in relation to chemistry with the notion of

corpuscular attraction as a precursor of affinity. He has been

regarded as one of the founders of nineteenth-century atomic

theory, and perhaps the very fact that the mighty Newton had

speculated in this way made atomism more respectable at a time

when the Cartesian system of science had passed into oblivion,

and many matter-of-fact chemists distrusted John Dalton as a

weaver of idle fancies. Certainly the less specialized corpuscularianand mechanistic concepts had the best chance of survival;

Cartesian mechanism, the dinosaur of seventeenth-centuryscientific thought, could not adapt itself to a new intellectual

environment. It was committed dogmatically in too many pointsof detail where it proved to be false.

Only with the passage of time, and usually in relation to pointsof precise detail, did the development of scientific activity in

Britain after the foundation of the Royal Society begin to follow

this definitely less specialized course, yielding a mechanistic

philosophy that was ultimately anti-Cartesian. More than twodecades passed, after the death of Descartes in 1651, before his

works acquired their greatest fame and authority, and before the

character of his system became rigid. Meanwhile, the prestige of

Gassendi was falling in France, and that of Descartes in Englandespecially through the success of new ideas concerning light

and gravitation. The Academic des Sciences became, before the1

Ibid., pp. 349-52.


end of the century, more deeply committed to Cartesian thought;the Royal Society more ready to criticize it. It is important to

realize that the somewhat singular character of the Royal Society

during its first half-century was due, not solely to the Fellows'

greater assiduity or success in experimentation emphasis on the

purity of their empiricism is certainly to be suspected but to

experimentation combined with a definite eclecticism of outlook,

within the broad framework of a mechanistic, corpuscularianscience which was becoming almost a commonplace. The intel-

lectual tension between the English scientific groups, on the one

hand, and the French and German on the other, certainly in-

creased between about 1665 and 1720, the substantial difference

between Cartesians and non-Cartesians being exacerbated by the

adventitious dispute between Leibniz and Newton over the inven-

tion of the calculus, but this should not be allowed to conceal the

fundamental similarity of their attitudes, on which Boyle had

insisted, and of their approach to scientific research. Although the

national organization of science facilitated a deplorable kind of

national partisanship most vicious in the early years of the

eighteenth century, beneath this there existed a fundamental

community of thought and activity. Broadly, the tendencies

of science were everywhere in the same direction, and in the

later eighteenth century, in a different situation, the friendly co-

operation between scientific societies was once more of the

greatest importance.

CHAPTER VIII

TECHNICAL FACTORS IN THESCIENTIFIC REVOLUTION

} I ^HE renaissance of science in the sixteenth century, and the

I strategic ideas of the first phase of the scientific revolution,JL owed little to improvements in the actual technique of

investigation. Before the beginning of the seventeenth centurythere is little evidence, except perhaps in anatomy and astronomy,of any endeavour to control more narrowly the accuracy of

scientific statements by the use of new procedures, still less to

extend their range with the aid of techniques unknown to the

existing tradition of science. Even the refinement of observation,

begun in anatomy by Vesalius and his contemporaries and in

astronomy by Tycho Brahe, hardly involved more than the natural

extension and scrupulous application of familiar methods. Since

the apparatus and instruments available were crude and limited

the means were not at hand for gaining knowledge of new classes

ofphenomena, or eliciting facts more recondite than those alreadystudied. Though greater reliance was placed on observation and

experiment, the change in the content of science could not be

dramatic and other sources of information were, at least till the

latter part of the sixteenth century, largely traditional. Aristotle,

Pliny, Dioscorides, Theophrastus and Galen were still very highly

respected. Gradually, however, the tendency to supplement this

book-learning, checked by personal examination where possible,

by the experience of various groups of practical men gained

ground. The wealth of fact was augmented by admitting the

observations of craftsmen, navigators, travellers, physicians, sur-

geons and apothecaries as worthy ofserious consideration, and thus

the status of purely empirical truths, hardly inferior to that of the

systematic truths of physics or medicine, was in time enhanced.

In this respect, as in others, the work of Galileo gives a useful

indication of a turning point, displaying in various ways the opera-tion of the new technical, as distinct from conceptual, factors

in the development of science. His practical, almost materialistic

217

ai8 THE SCIENTIFIC REVOLUTION

intellect, stripping from natural philosophy the vestiges of its

metaphysical connotations, led him to admire the technologicalachievements of his time and to appreciate the scientific prob-lems suggested by them. By revealing the value of mathematics

as a logical instrument in scientific reasoning, he transformed,if he did not actually create, an important method of inquiry.His exploration of the potentialities of the telescope and other

instruments shows his concern for the enlargement of the scope of

observation and experiment through newly invented techniques.It is typical of the evolution of the apparatus of science during the

seventeenth century that Galileo's results were more notable for

their qualitative originality than for quantitative accuracy, since

the necessity for precision in measurement was less apparent than

the strange novelties which the new techniques unfolded. Thoughthe perspective in which science regards nature changed markedlyin the sixteenth century, it was only in the seventeenth that a sig-

nificant qualitative change occurred in the image itself, to which

the technical resources used by Galileo contributed profoundly.It has already been pointed out that the ideal of social progress

was also a commonplace among seventeenth-century scientists,

and that with varying degrees of assurance the attainment of this

ideal was linked with the application of scientific knowledge to

technology. Conversely, it is clear that scientific research is itself

dependent upon the level of technical skill, especially when the

endowment or organization of science compel the experimenterto rely upon the skills acquired by the craftsman in the normal

course of his trade, as was the case before the nineteenth century.

Perhaps, in the early stages of a science, it is even more importantthat the investigator should be amply provided with both prob-lems and the materials for solving them by the technological

experience to which he has access. This is partly a question of

attitudes the ability to receive the stimulus from a merely

practical quarter partly of the richness of the techniques. Galileo

makes Sagredo remark, on the first page of the Discourses:

I myself, being curious by nature, frequently visit [the Arsenal at

Venice] for the mere pleasure of observing the work of those who, onaccount of their superiority over other artisans, we call

"first rank

men.*' Conference with them has often helped me in the investigationof certain effects including not only those which are striking, butalso those which are recondite and almost incredible. At times also

TECHNICAL FACTORS 219

I have been put to confusion and driven to despair of ever explaining

something for which I could not account, but which my senses told

me to be true.

It can hardly be doubted that the dialogue of the First Day in this

work was influenced by such practical observation, and it was

from a workman that Galileo learnt of the break-down of the

honor vacui theory when the attempt was made to lift water throughmore than thirty feet by means of a suction pump. Bacon also

wrote of the knowledge concealed in skilled craftsmanship. In the

next generation Boyle thought that only an unworthy student of

nature would scorn to learn from artisans, from whom knowledgecould best be obtained; for

many phenomena in trades are, also, some of the more noble anduseful parts of natural history; for they show us nature in motion,and that too when turn'd out of her course by human power; whichis the most instructive state wherein we can behold her. And, as the

observations hereof tend, directly, to practice, so may they also afford

much light to several theories. 1

Such opinions did not spring from theoretical reasoning alone.

They express the new philosophy's concern for realia, but they also

recognize a genuine historical fact, that many of the ordinary

operations of household and workshop were quite beyond the

reach of scientific explanation. To remedy this, Galileo began the

theory of structures and Boyle the study of fermentation in food-

stuffs. Many of the problems suggested by the "naturalist's insightinto trades" could not, of course, be very profitably handled in

the seventeenth century and some of the most intractable like

fermentation were in any case very old. On the other hand, the

inquiry into geomagnetism begun in the late sixteenth century is

an example of a branch of science originating in the recent

observations of practical men and followed up with profit to both

theory and practice. Time-measurement also was both a scientific

and a commercial problem, especially in relation to navigation.More obviously, skill in glass- and metal-working, especially

grinding, turning and screw-cutting, could be readily applied to

scientific purposes. Improvements in such arts were sought

by scientists and craftsmen together, as when Robert Hookecollaborated with the famous clock-maker, Thomas Tompion.

1 Considerations touching the Usefulness of Natural Philosophy; Shaw's Abridge-

ment, vol. I, pp. 129-30.


In three related sciences, chemistry, mineralogy and metallurgythe pre-eminence of art over science was very marked at the

opening of the sixteenth century. In natural philosophy there was

a rudimentary knowledge of the classification of gems, earths andores together with a wholly useless theory of the generation and

transformation of substances. The pseudo-science, alchemy, had

its own theory ofthe nature ofmetals and their ores, and contained

some sound information on chemical processes and the preparationof simple inorganic compounds. But during the previous three

centuries its originally useful content had become garbled and

obscured through the growth of esoteric mysticism and the

propagation of absurdities in its name. By contrast, great progressin chemical industry, at a time when this represented almost the

only rational body of chemical knowledge, was scarcely reflected

at all in scientific writings before the mid-sixteenth century. There

were changes, permitting the use of new materials, economy of

manufacture, or the improvement of the product, in a long list

of trades, all of which depended on chemical operations, such as

the extraction of metals and the refining of precious metals, glass-

and pottery-making, the manufacture of soda and soap, the re-

fining of salt and saltpetre and the manufacture of gunpowder,the preparation of mineral acids, and distillation. Other chemical

arts, like dyeing and tanning, were probably less improved; somelater innovations, like sugar refining, immediately aroused scien-

tific interest. The knowledge of the craftsmen concerned was, of

course, wholly empirical; they were uninterested in theory, and

given to superstition and prejudice. Part of their skill may have

derived from the Greek scientific tradition through Islamic

sources the art of distillation was clearly derived in this way,but it was perfected by artisans, not by philosophers or alchemists.

Much of their skill was the tardy fruit of long experience. Taken

altogether, craft knowledge in chemistry and related sciences im-

plied a far greater acquaintance with materials and command over

operations than were available to the philosopher or the adept.

By the end of the sixteenth century something like a rational

chemistry was coming into existence, though sixty years later

Boyle could still write:

There are many learned men, who being acquainted with chymistrybut by report, have from the illiterateness, the arrogance and the

impostures of too many of those, that pretend skill in it, taken


occasion to entertain so ill an opinion as well of the art as of those

that profess it, that they are apt to repine when they see any person,

capable of succeeding in the study of solid philosophy, addict himself

to an art they judge so much below a philosopher . . . when theysee a man, acquainted with other learning, countenance by his ex-

ample sooty empirics and a study which they scarce think fit for anybut such as are unfit for the rational and useful parts of physiology

[science].1

In the course of that century a number of books had appearedwhich, although primarily concerned with technological processes,

had a significant influence on the chemical group of sciences.

Avoiding theory, they threw off the air of mystery. They described

in a matter-of-fact way how mineral substances were found in

nature, extracted, and prepared, and how further commercial

products were obtained from them by the operations of art. The

processes described required mineralogical and chemical know-

ledge, manipulative skill, and often a complex economic organi-zation. Some of the German mines already absorbed heavy

capital expenditure, and some processes, like the manufacture of

nitric acid needed for the separation of gold from silver, were

conducted on a considerable scale.

The first of these treatises was a small German work known as

the Bergbiichlein, printed at Augsburg in I5O5.2 Before this, in the

fifteenth century, there had been in circulation manuscriptswritten in German dealing with pyrotechnics, the preparation of

saltpetre and the manufacture of gunpowder, but these were never

printed and seem to have been unimportant in science. Possibly

there were similar "handbooks," earlier than the invention of

printing, dealing with mining and metallurgy. The Bergbuchlein

describes briefly the location and working of veins of ore, and is

followed in the Probierbiichlein (first printed about 1510) by an

account of the extraction, refining and testing of gold and silver.

Their usefulness is proved by the many editions published. Thesame subjects were treated by Biringuccio in 1540, by Agricola in

1556, and by other German authors later in the century. The best

informed of these was Lazarus Ercker, superintendent of the mines

in the Holy Roman Empire, whose Treatise on Ores and Assaying

1 Works (ed. Birch, 1772), vol. I, p. 354.* A. Sisco and C. S. Smith: Bergwerk- wd Probierbiichlein (New York, 1949).

Cf. also Anneliese Sisco in Isis, vol. 43, 1952.


(Prague, 1574), was translated into English as late as I683.1

Broker's thoroughly practical book is chiefly concerned with the

precious metals, but has chapters on working with copper and

lead, on quicksilver, and on saltpetre. The Pirotechnia of Vanoccio

Biringuccio and the De re Metallica of Agricola both cover a wider

range of topics.2Biringuccio, for instance the only Italian author

of an important work of this type describes the blast furnace,

bronze- and iron-founding, and glass manufacture, but the tech-

nical information is somewhat unspecific. Agricola's book, mas-

sively detailed in its account of geological formations, mining

machinery and chemical processes is justly regarded as the master-

piece of early technological writing. Agricola [germanice GeorgBauer] was a scholar, corresponding with Erasmus and Melanch-

thon, writing good Latin, enriching his observations with appro-

priate quotations from classical authors. He wrote also On the

Nature of Fossils and on other scientific subjects. His knowledge of

mining and industrial chemistry was gained through long resi-

dence, as a physician, in the mining towns of Joachimsthal in

Bohemia and Chemnitz in Saxony. About the first third of De re

Metallica is given to a discussion of mining methods. Then Agricola

passes on to describe the assaying of ores to determine their

quality, and the operations of preparing and smelting them.

Iron, copper, tin, lead, bismuth, antimony and quicksilver are

considered as well as the precious metals. The testing of the base

metals for gold and silver content is the next topic, followed byan account of the separation of precious and base metals, andof gold from silver. Here the various processes of cupellation,

cementation with saltpetre, liquation with the use of lead, amal-

gamation with mercury, refining with stibnite, and extraction

with what Agricola calls aqua valens are described at length. This

last was, apparently, a mixture of mineral acids prepared bydistillation of different mixtures of vitriols, salt, saltpetre, alumand urine. The last section of the work treats of the preparationof "solidified juices" salt, potash and soda, alum, saltpetre,

vitriols, sulphur, bitumen and glass. Here Agricola was on less

firm ground and was guilty of some confusion and error.

1 Modern translation by A. Sisco and C. S. Smith (Chicago, 1951).1 The former translated into English by M. Gnudi and C. S. Smith (New

York, 1943); the latter by H. C. and L. H. Hoover (London, 1912; New York,1950).


This series of technical books reflects a tradition in appliedscience that had grown slowly in the later centuries of the middle

ages, that was still gradually increasing in skill, and was capableof producing new techniques for handling the unprecedentedrichness of the South American mines. The authors, like the

contemporary anatomists and herbalists, took full advantage of

the art of wood-cut illustration. They did their work so well that

it lasted into the early eighteenth century, when a new era of

technology was beginning; it was over Agricola's great folio that

Newton pored when he was investigating the chemistry of metals.

Chemical industry did not merely furnish the chemists of the late

sixteenth and seventeenth centuries with the materials in their

laboratories; it supplied them with a factual account of the

occurrence of minerals in the natural state and the methods of

their preparation. More than this, the technical treatises provided,in contrast with the fanciful symbolic language of the alchemists,

a precise account of basic chemical operations and reactions.

Besides the works already mentioned, the philosophical chemist

and virtuoso could turn to the Distillation-book of HieronymusBrunschwig (1512) and its successors for instruction in this most

necessary, and most difficult, of chemical arts. The alchemists,

even when honest, wrote on the principle that if the reader hadnot been admitted to the secrets he would fail to understand, andif he had he would scarcely need further guidance. These writers,

however, set forth the best of their knowledge as plainly as

possible; and it was likely to be sound, for as Boyle remarked,'

tradesmen are commonly more diligent, in their particular way,than any other experimenter would be whose livelihood does not

depend on it.' Only in its practical applications, stripped to its

bare essentials of preparing this from that, was chemistry on a

really solid foundation, independent of the misleading implica-tions of false, and often fantastic, theories. But the chemical

operations of industry were not merely qualitatively reliable andinstructive. The application of quantitative methods to a chemical

reaction was the essence of assaying, for example in calculatingthe quantity of gold in an alloy by carefully drying and weighinga precipitate.

The assayer deserves as much credit as the observational astronomer

for providing numerical data and establishing the tradition of accu-

rate measurement without which modern science could not have


arisen. Though more of a craftsman than a scientist and more con-

cerned with utility than with intellectual beauty, the assayer never-

theless collected a large part of the data on which chemical science

was founded. 1

When, in the eighteenth century, the balance was recognized as

an invaluable tool in research the chemist was only extendinga technique whose specialized usefulness in assaying was longfamiliar. Even the law of the conservation of mass was no morethan a theoretical statement of a truth on which the operationsof this craft were founded.

Boyle once spoke of German as the "Hermetical language,"because so many alchemists had used it. It is perhaps a more useful

observation that rational chemistry began with accounts of the

elaborate chemical industry in Germany, and was continued byGerman experimenters, some of them inspired by Paracelsus,

himself a German-Swiss. Here there seems to be a clear case for

believing that the development of a technical art to the necessary

point in complexity and achievement provided much of the basis

of fact and method from which experimental sciences could

arise. Of course, the roots of modern chemistry, mineralogy and

metallurgy are also to be found in alchemy, in pharmacy, and in

philosophy. To the formation of chemical theories in the seven-

teenth and eighteenth centuries the description of practical opera-tions contributed very little. Ideas were derived from different

sources; and there was even a muddled, wrong-headed tradition

of laboratory work in alchemy parallel to operations on the in-

dustrial scale. Yet in many ways the outlook of Black or Lavoisier

resembles that of a practical assayer more than it does the esoteric

perspective of Raymund Lull, Paracelsus or "Basil Valentine."

The influence of the artisan, conceived as closer to the realities

of nature than the abstracted philosopher, was an importantelement in many of the nascent sciences, but nowhere morethan in chemistry, which most of all required an alliance of sane

thought and reasoned activity.

In the second aspect of the role of technical factors in the

scientific revolution, the technique of mathematical analysis offers

a good example of a factor internal to science itself influencingthe progress of certain branches, in this instance mechanics and

1 Smith: Lazarus Ercker's Treatise on Ores and Assaying (Chicago, 1951), p. xv.


astronomy. In a similar manner chemistry was another internal

factor affecting the progress of physiology, but this was scarcely

realized as yet. The ambition to formulate theoretical propositionsand experimental results in the form of mathematical functions,

nourished in some men by reflections of Platonic or Pythagorean

philosophy, was commonly entertained in the seventeenth century,even by those little learned in mathematics. As Boyle foresaw, 'A

competent knowledge in mathematics is so necessary to a philo-

sopher that I scruple not to assert, greater things are still to be

expected from physics, because those who pass for naturalists have

been generally ignorant in that study.'1 The singularly happy

synthesis of mathematical reasoning and experiment in geo-metrical optics and mechanics was regarded as a model to be

imitated in other parts of science, and it was recognized that a

mathematical demonstration has a rigour, and sometimes a

generality, not easily obtained in other arguments. The study of

mathematics, for the sake of its beneficent effect upon the intel-

lectual powers, as an introduction to natural and moral philo-

sophy, and as a necessary preliminary to certain professions, was

by degrees granted a more prominent place in education. It was

readily seen that the practical sciences navigation, cartography,

surveying, gunnery owed their origin to the combination of

mathematical method with more exact instrumental measure-

ment. They had thus gained a certainty impossible with rule-of-

thumb procedures. About the middle of the seventeenth centuryit was found that the vagaries of chance, in the throw of a die or

the odds in betting, were not immune to the laws of mathematics.

The calculus of probabilities was begun. Closely connected with

this were the first essays in statistical analysis, byJohn Graunt andSir William Petty in England, which proved that even the hazards

of human life were not beyond computation. From such crude

beginnings developed an impressive mathematical apparatus of

immense importance to theoretical physics in the nineteenth

century.These analogies, of very different kinds, suggested that where

quantitative observation and experiment were possible, a mathe-

matical formulation ought to be adopted. Galileo had shown the

splendour of the prize that might be won. Ifthe workings of nature

1Usefulness of Natural Philosophy; Philosophical Works, abridged by Peter Shaw,

vol. I, p. 118.

in


were regular and uniform, should not they ultimately reveal a

mathematical harmony, as Kepler thought? In the study of acous-

tics, during the seventeenth century, it was indeed found that

harmonies pleasing to the ear were produced by the vibrations of

different strings when their lengths, thicknesses and tensions agreedwith simple mathematical ratios. More generally, Cardano in the

sixteenth century had reviewed the physical applications of the

rules of proportion, while Petty examined, in a paper in the Philo-

sophical Transactions, the special significance of the quadratic ratio

nature[that is, functions of the type a = kb*

ya = --

j. Again,

if the mechanical philosophy was justified in its belief that the

physical properties of macroscopic bodies result from the shape,size and motion of the particles composing them, ought not all

these properties of the particles to be susceptible of mathematical

discussion, which was already making great progress with the

study of motion? And, indeed, by making certain measurements

in connection with the phenomenon of optical interference, and

examining them mathematically, Newton was able to make

quantitative statements about the nature of light. Furthermore,mathematical analyses enabled him to prove that some conse-

quences of the Cartesian theory of matter were quite incompatiblewith observation.

The limitations to the extension of the mathematical method,

flourishing in dynamics, to the whole of physics and a fortiori to

still less "exact" parts of science were obviously oftwo kinds. Thefirst lay in the ability of physicists and others to design experi-ments and produce results of a form suitable for mathematical

analysis; the experimental physicist had to discover in what waysmathematics could help him before he could become a mathe-

matical physicist. This kind of limitation had vitiated all attemptstowards a mathematical theory of projectiles before the time of

Galileo.1 The second limitation is in the nature of mathematics

itself, in its ability to perform the operations required. For ex-

ample: Boyle's experiment on the compression of a volume of air

in one limb of a U-tube by a column of mercury poured into the

1 The parabolic trajectory of a projectile in a vacuum was first established

by Bonaventura Cavalieri in Lo Spccchio Ustorio (1632), six years before Galileo's

much fuller treatise appeared. The problem was easily solved mathematicallywith the aid of Galileo's theorem on acceleration.


other (described in A Defence of the Doctrine touching the Spring and

Weight of the Air, 1661) gave quantitative results which could be

simply interpreted to yield "Boyle's Law" (pv = k). It was also

found that the height of the mercury column in a barometer falls

as the instrument is carried progressively higher above sea-level,

because the weight of the atmosphere above decreases. The cele-

brated experiment was carried out by Pdrier, on the suggestion of

Pascal, in I648.1 From a combination of these facts, it was realized

that it should be possible to frame a mathematical theory whichwould enable the vertical distance between two stations to be

calculated from the difference in atmospheric pressure found from

simultaneous readings of two barometers. To make a rough ap-

proximation is sufficiently easy, but an accurate calculation

involved purely mathematical difficulties which were not fully

overcome in the seventeenth century.Discussion of the first group of these factors limiting the applica-

tion of the mathematical method to science must, naturally,

belong to the history of the separate branches of science. It wouldbe necessary to discuss, in each case, the steps by which experi-ments were designed and instruments invented to obtain quanti-tative results of various types, and the methods followed in the

formulation of a variety of theoretical postulates, before materials

suitable for mathematical study were assembled. Till the nine-

teenth century no parts of science, other than mechanics and

astronomy, were so highly organized and coherent that the appli-cation of mathematics was possible, otherwise than in elementary

computations. But with regard to mechanics and astronomy the

second limitation latent in the resources of mathematics itself

becomes significant; the great achievements which signalized the

triumph of the scientific revolution would have been impossiblein the absence of the enormous elaboration of pure mathematics

which took place, and was to some extent inspired by realization

ofthe fact that it was essential. Nearly all the great mathematicians

of the sixteenth and seventeenth centuries, from Tartaglia andStevin to Cavalieri, Descartes, Newton and Leibniz, were at least

partly interested in the physical sciences. One of the unexpected

1 Pascal deduced that the atmospheric pressure would fall progressivelyabove sea-level from his own repetition of Torricelli's experiments with the

barometer. The deduction was confirmed by Pe'rier's ascent, with the instru-

ment, of the Puy-de-D6me, in Auvergne.


discoveries of the time was that a number of regular mathematical

curves (some long familiar), such as the ellipse, the parabola and

the cycloid, or the algebraic functions which Descartes associated

with such curves, appeared in the investigations of the astronomer

and the physicist, so that their study proved to have a double

interest. The calculations performed by the physical scientist fre-

quently required the calculation of an area bounded by a curve

of some type, and so in turn stimulated investigation of the opera-tion of integration in which perhaps the success of seventeenth-

century mathematicians was most striking. A number of their

advances in method w?re first denoted by the solution of some

problem in mechanics, which offered from about 1650 onwardsa most rewarding opportunity for the display of mathematical

inventiveness, formerly more commonly devoted to the improve-ment of the mathematical procedures in astronomy.

1

The progress made in mathematics in the seventeenth centurycan be very easily illustrated from the fact that, about 1600, it

had hardly as yet reached a form intelligible to modern eyes. The

writing of Arabic numerals was indeed nearly stabilized in the

modern style, but the Roman were still commonly employed,

especially in accounting. The use of the modern symbols for the

common operations of multiplication, division, addition and so

forth was standardized only in the second half of the seventeenth

century. Previously mathematical arguments were set out in a

diffuse rhetorical form. Algebraic notation was settled at about

the same time, the practice of employing letters to denote un-

known or indeterminate quantities having been introduced by the

French mathematician Vtete shortly before 1600. Arithmetical

operations, particularly those involving long division or the hand-

ling of fractions, were still performed by cumbersome methods,and "reckoning with the pen" (rather than with the abacus

or other aid) was still regarded as a somewhat advanced art. Oneof the earliest calculating-devices, the so-called "Napier's bones,"was designed to obviate the memorization of multiplication tables

and the labour ofhandling long rows of figures. Again, at a higher

level, tables of functions were very deficient. In trigonometry, the

1 It has been pointed out that almost all the progress made in the theory of

structures, for instance, before about 1 770, was made as a by-product of sheermathematical ingenuity. The same might be said of the applied science of

ballistics, which also had a negligible experimental foundation before 1 740.


Greeks had known tables of chords alone; during the late middle

ages tables of sines and tangents became available, and during the

sixteenth century other trigonometrical functions were tabulated.

But the methods of computing and of using the tables were both

very tedious. From an attempt to facilitate calculations involvingthese functions developed the invention oflogarithms, perhaps the

most universally useful mathematical discovery of the seventeenth

century, as it was certainly the least expected. Napier's tables,

published in 1614 (Mirifici logarithmorum canonis descriptio), gave

logarithms of sines which are effectively powers of a base tf"1

,the

reciprocal of the base of modern Napierian logarithms.1 A table

of logarithms to the base 10 for the first thousand numbers was

published by Henry Briggs in 1617. Logarithms offered a com-

pelling instance of the utility of the decimal system of fractions,

of which Stevin had been a most forceful advocate some thirty

years earlier.

Since the Greeks had excelled in geometry and trigonometry,little more than the assimilation, with some slight extension, of

their methods in these branches of mathematics had been accom-

plished by 1600. Renaissance scholarship had devoted itself to the

recovery of the pure classical tradition in this as in other depart-ments of learning, with the result that the texts, particularly those

describing the more advanced Greek studies of geometrical analy-sis and the conic sections, were far more completely available bythe middle of the sixteenth century than before. Here, at least,

pure scholarship caused an immediate rise in the level of com-

petence. Even in the mid-seventeenth century the practice of

"restoring" a lost or fragmentary work by means of the methods

presumably used by the ancient author did not seem absurd, andwhen Newton wrote the Principia the synthetic geometry of the

Greeks was still held to be a more reliable form of mathematical

demonstration than the recently developed analytical method.

Algebra, on the other hand, represents a native European de-

velopment from Hindu and Islamic sources made known to the

Latins by medieval translators. Considerable progress in the

sixteenth century, for example in the solution of equations of

higher powers than the quadratic, was unaffected by humanistic

influences; indeed, Greek geometric procedures for solving equa-tions were supplanted by algebraic methods. Operations with

1 Hence logNa = 2'3O259log10fl.


proportions and series, also known to the Greeks solely in the

geometric form, were similarly transformed into the more con-

venient algebraic symbolism. Islamic mathematicians (notablyOmar Khayydm, c. noo) had recognized a partial equivalencebetween algebra and geometry, that is, that certain geometrical

problems could be represented by algebraic functions; and this

equivalence was more thoroughly exploited by the Europeanmathematicians of the sixteenth and early seventeenth centuries.

The next step, upon which analytical geometry is founded, was

the representation of any function graphically by the use of

rectangular co-ordinates. Graphs with such co-ordinates had been

used in the middle ages for a few special purposes (e.g. to repre-sent the motions of the planets), and Oresme's calculus of varying

qualities was itself an elementary form of co-ordinate geometry.Far more general and precise methods had been sketched in

private by the English mathematician Harriot, and by Pierre

Fermat, before the publication of the first treatise on the subject

by Descartes the GeomStrie annexed to his Discourse on Method

(1637). In this he showed that a constant relationship exists be-

tween the co-ordinates x andj> of any point on a regular mathe-

matical curve which can be expressed as the algebraic function

y =f(x), and that certain patterns of function corresponded

uniformly with certain classes of curves.

This discovery was capable of immediate and fruitful applica-tion to mechanics, in which many problems could be most easily

postulated in an initial geometric form, and then analysed with

the aid of the appropriate algebraic functions. Thus, to cite a

simple instance, in ballistics it was no longer necessary by the

end of the seventeenth century to work out a range by supply-

ing the necessary constants in the geometric construction used

by Galileo, since it could be obtained directly from the function

y = x tan eJ

appropriate to the parabolic trajectory, from which all the

theorems established by the elaborate geometry of Galileo andTorricelli are readily deduced. Such functions can, of course, be

derived far more easily by use of the differential and integral

calculus than by the application of algebraic notation to conven-

tional geometrical reasoning, and the usefulness of the "calculus"

to the engineer and technician as well as to the mathematical


scientist has therefore been clearly recognized since about the

middle of the eighteenth century. Both Kepler (1616) andCavalieri (1635) made use of infinitesimals in integration, the

former in connection with practical problems such as the calcula-

tion of the volumes of casks. Thus Cavalieri imagined that the

area of a surface was made up of an infinite number of lines, andthe volume of a solid ofan infinite number ofsuperposed surfaces,

calculating these quantities by the summation of an infinite

number of their geometric elements. Such methods had a certain

practical value, but the concepts were badly defined and of

doubtful validity. In co-ordinate geometry the problems for

which they were designed were first set out in the modern syste-

matic form. Perhaps even more important were the methods for

finding the maximum and minimum values of curves (or the

equivalent functions), and for drawing tangents to them, dis-

covered by Fermat (1638) and others about the middle of the

century, for they used operations identical in principle with whatwas later known as differentiation. Barrow, for example, in his

method of tangents, obtained by geometrical means the derivative

f-j- J

of the function (y=f(x)) represented by the curve, and

equated this derivative to zero.

Before 1670, therefore, the crude components of new mathe-

matical processes for dealing with quantities having a non-linear

variation were already in existence. The priority in time in

perfecting them undoubtedly belongs to Newton (whose Method

ofFluxions was written in 1671), but a more useful notation and a

somewhat clearer presentation of the matter were later developed

independently by Leibniz, whose first essay on the calculus was

published in 1684. The charge maintained by a group of English

mathematicians, with considerable covert assistance from Newton

himself, that Leibniz had plagiarized Newton's ideas from un-

printed manuscripts which had circulated privately provoked in

the early years of the next century a sordid and bitter disputebetween them and most continental mathematicians. Its only

significance is that the transmission to England of continental

discoveries in pure and applied mathematics was inhibited for

over a century, until soon after 1830 the Newtonian method of

fluxions was replaced by the virtually equivalent differential and

integral calculus which had advanced very far from Leibniz*


original invention. 1 In principle, both Leibniz and Newton were

successful in the same task: they generalized the methods of

differentiation and integration which were already in existence,

recognizing that the latter operation was the inverse ofthe former;

they developed the new notation required for these new opera-

tions; and they greatly clarified mathematical thinking about

their nature. Both succeeding in solving by the new methods

problems which had been nearly intractable to the old.

The first coherent treatise explaining the calculus was onlywritten at the close of the seventeenth century, and its generalextension to mechanics and physics was the work of more than

one succeeding generation. Consequently its full impact on science

was not immediate, though Newton referred in passing to his

method of fluxions in the Principia and the mathematical demon-strations he offered would have been impossible without it.

Nevertheless, mathematical methods tending towards those of the

generalized calculus, or even anticipating it, were widely appliedin mechanics from about 1650 onwards, along with other new

developments in advanced algebra (for example, the study of

series) . Huygens offers perhaps the neatest instance of a physicist

making by means of co-ordinate geometry many complex calcula-

tions that would now be dealt with by means of the calculus,

through the development of his own methods which were virtually

equivalent to differentiation and integration. In this way Huygenswas able to investigate some of the properties of motion in a

resisting medium, which were also examined (rather more

thoroughly) by Newton in Book II of the Principia with the aid of

fluxions. It seems that, with the exception of celestial mechanics,the development of no branch of science was seriously obstructed

by the absence of a suitable mathematical technique, even before

the formulation of the true calculus. Some known problemsremained unsolved, naturally, partly owing to imperfect concep-

tualization, but partly also owing to the fact that their solution

1 The truth seems to be that Leibniz was in close contact with men whounderstood something of Newton's new ideas; that he saw some of Newton's

manuscripts; but that he could have learned little in this way that he could nothave gathered from other sources, and that his ideas were already at the

significant time shaping towards the form in which they were later formulated.

Leibniz has long been cleared of the charge of plagiarism; any historical

obscurities that remain are of little significance. (For bibliography cf. D. E.Smith: History of Mathematics, vol. II, p. 691.)


required difficult approximations involving constants which hadnot yet been determined experimentally. On the contrary, it

seems rather that the nature ofthe possible mathematical processesexercised a powerful guiding influence at least over the science of

mechanics. Even had ideas been more precise, and the experi-mental material more complete, it would have been impossiblefor the seventeenth-century physicist to work out a mathematical

corpuscular theory of matter because he lacked the necessary

technique of statistical analysis; but mechanics acquired an

increasingly theoretical character because its problems could be

stated mathematically, and solved by known procedures. The

propositions of the Principia are not less certain, although they

may not be the result of mathematical analysis applied to a mass

of experimental data; but it must be recognized that Newton's

method was to deduce, by mathematics, the consequences of

selected axioms and then to show by reference to observation or

experiment that these consequences are actually confirmed in

nature. Already in Galileo's writings it is apparent that in science

the mathematical and experimental approaches are far from

identical, though they may be closely correlated. He himself

attached greater importance to his mathematical theories than to

his experimentation (which is never precisely described, and often

appears casual). The early researches of the scientific societies laid

a greater emphasis on exactitude and consistency in experiment;but mechanics was again sublimated into the regions of highermathematics in the last years of the century. The consequence of

this may be illustrated by Huygens' ingenious proof that a pendu-lum is perfectly isochronous when describing a cycloidal arc a

discovery, made with the object of perfecting the mechanical

clock, which proved completely irrelevant to the experimentalsearch for a scientifically reliable time-keeper; or by the history

of the industrial revolution, which was scarcely at all promoted bythe elaboration of theoretical mechanics during the eighteenth

century. There was, in fact, a strong tendency for the first truly

mathematical branch of science to lose touch with its roots in

experiment by becoming no more than a specialized departmentof mathematics.

It may perhaps seem surprising that seventeenth-centurymathematics progressed so opportunely as to satisfy, very largely,

all the demands that science made upon it. Only the activity of


a number of highly original mathematicians made this possible,

and obviously their activity was not wholly fortuitous (it is re-

markable, for instance, that there was so little interest in the theoryof numbers) . It was inspired, to some extent, by knowledge of the

usefulness in science of advances in certain directions. But it is

generally true, of other periods as of this, that the mathematics

required for any particular step in science has been available.

Greek science was never near to exhausting the subtlety of the

Greek mathematician. In recent times the mathematics of the

theory of relativity was in being well before Einstein. Perhaps this

empirical fact, more than anything else, justifies the qualification

of mathematics as a scientific technique. When a class of facts, or

concepts, is first subjected to its use, the mathematics involved

will tend to be relatively simple, if only for the reason that the

innovator will probably be a scientist, more familiar with the

science than with the most recent advances in mathematics itself.

Galileo was not a great mathematician. But as the mathematical

theory develops, its continuance will increasingly depend uponthe activity of men who have been trained as mathematicians to

digest and analyse the results of experiment, even to suggest and

perhaps carry out the experiments and measurements necessaryfor the! prosecution of the theory. Yet it will rarely happen that

the mathematician who applies his skill in this way penetrates to

the very frontiers of pure mathematics. While the application is

perfected, mathematics itself is not standing still. And the appli-cation is made because the mathematical theorist perceives that

the particular technique is appropriate, or adaptable, to the

problem. The conjunction of the highest mathematical with the

highest scientific ability, as in Archimedes or Newton, is extremely

rare; the fabrication of scientific theory by the use of well-known

procedures has, on the other hand, been a frequent occurrence.

The invention of numerous scientific instruments during the

seventeenth century, and their fertile use in many capacities, has

long been associated with the revolution in scientific thought andmethod. The idea of science as a product of the laboratory (in

the modern sense of the word) is indeed one of the creations of

the scientific revolution. In no previous period had the study of

natural philosophy or medicine been particularly linked with the

use of specialized techniques or tools of inquiry, and though the


surgeon or the astronomer had been equipped with a limited

range of instruments, little attention was paid to their fitness for

use or to the possibility of extending and perfecting their uses.

More variants of the astrolabe, the most characteristic of all

medieval scientific instruments, were designed during the last

half-century of its use in Europe (c. 1575-1625) than in all its

preceding history. The Greeks had known the magnifying powerof a spherical vessel filled with water, but the lens was an inven-

tion of the eleventh century, the spectacle glass of the thirteenth,

and the optical instrument of the seventeenth. Navigationalinstruments also were extremely crude before the later sixteenth

century. It was not that ingenuity and craftsmanship were wholly

lacking (for many examples of fine metal-work, for artistic and

military purposes, prove the contrary); rather the will to refine

and extend instrumental techniques was absent. On the other

hand, it has justly been pointed out that the early strategic stagesof the scientific revolution were accomplished without the aid of

the new instruments. They were unknown to Copernicus, to

Vesalius, to Harvey, Bacon and Gilbert. They leave no trace in

the most important of Galileo's writings, in which he reveals

himself driven to measure small intervals of time by a device

considerably less accurate than the ancient clepsydra. It is clear

that, great as was the influence of the instrumental ingenuity of

the seventeenth century upon the course of modern science, such

ingenuity was not at all responsible for the original deflection of

science into this new course.

Thus it would seem that the first factor limiting the introduction

into scientific practice of higher standards of observation and

measurement, or of more complex manipulations, lay in the

nature of science itself. Only when the concept of scientific re-

search had changed, as it had by the end of the first quarter of

the seventeenth century, was it possible to pay attention to the

attainment of these higher standards. A number of the new instru-

ments of the seventeenth century were not the product of scientific

invention, but were adopted for scientific purposes because the

new attitude enabled their usefulness to be perceived. The balance

was borrowed from chemical craftsmanship. The telescope was

another craft invention, initially applied to military uses. The

microscope was an amusing toy before it became a serious instru-

ment ofresearch. The air pump in the laboratory was an improved


form of the common well pump Otto von Guericke, its original

inventor, had at the beginning exhausted vessels by pumping out

water with which they had been filled. And inevitably the tech-

niques used in the construction of the new scientific instruments

were those already in existence; they were not summoned out of

nothing by the unprecedented scientific demand. Some instru-

ments were only practicable because methods of lathe-turningand screw-cutting had been gradually perfected during two or

three centuries, partly owing to the more ready availability of

steel tools, others, because it was possible to produce larger,

stronger and smoother sheets or strips of metal. The techniquesof glass grinding and blowing which provided lenses and tubes

might have been turned to scientific use long before they were.

The established skill of the astrolabe-maker could be devoted to

the fabrication of other instruments requiring divided circles and

engraved lines, that of the watch-maker to various computers andmodels involving exact wheel-work, and so on. Common crafts-

manship held a considerable reservoir of ingenuity, when scientific

imagination arrived to draw upon it.

On the other hand, once interest in the kind of result that could

be obtained from the employment of specialized instruments hadbeen created, particularly as this employment began to extend

under a more disciplined direction towards a greater qualitative

depth of information and a greater quantitative accuracy of

measurement, the limitations of normal craftsmanship were soon

reached. Then it was necessary to begin a more conscious exami-

nation of the instruments themselves. Descartes was virtually the

founder of the scientific study of the apparatus of science, in his

investigation of the causes of the distortions present in the imagesofcrude microscopes. (At the same time, purely empirical measures

were also being adopted to remedy their defects.) Descartes con-

cluded that lenses should be ground to a non-spherical curvature,which would introduce greater complexity into their manufacture.

Some scientists (including the astronomer Hevelius, and the

microscof)ist Leeuwenhoek) became masters in the art of grindingthe lenses they required for their work; others, like Newton,

experimented with an alternative form of optical instrument.

Towards the end of the century a scientist wishing to have a

really good telescope or microscope could no longer simply makeuse of craftsmanship; he had to direct the work in accordance


with a pre-determined specification. Astronomy had already at

the end of the sixteenth century reached the point where further

advances in precision involved great effort. Devices like the

vernier scale and the tangent screw were major steps, and the

attachment of telescopes to instruments for measuring anglesreduced sighting errors. But the advantages gained by increased

complexity in mechanical construction were all dependent on

progressive refinement in workmanship, and the forethought and

supervision of the scientist. The astronomer, in fact, had to

consider his observatory as an exercise in design; he had to build

walls, duly orientated, that would not settle; to design quadrantsthat were rigid, yet light, and true; to ascertain the probableerrors of divided scales; to collimate his telescopes and rate his

clocks. He had become aware that the limitations to his workwere imposed by factors that were, in the main, technical andmechanical. As such, they deserved, and received, increasinglymeticulous attention.

From the historical point of view, instruments may be divided

into two classes: those which render qualitative information only,and those which permit ofthe making ofmeasurements. Naturally,these uses of an instrument are not necessarily exclusive, in fact a

little consideration makes it obvious that in their evolution most

early scientific instruments tended to move into the second class.

Thus, devices like the micrometer could be added to telescopes

and microscopes so that very small or very distant objects could

be measured; or alternatively these optical systems could be addedto other measuring instruments to improve their performance.But thefirst use was purely qualitative. Similarly, in the eighteenth

century, the electrometer designed in the first place for the detec-

tion ofcharges, was later applied to their comparison and measure-

ment. The balance was first used in chemistry to establish a simpleloss or gain in weight; its employment to determine accuratelythe masses involved in a chemical reaction came much later.

It is therefore a natural and plausible proposition that the quanti-tative potentialities of a new instrument or piece of apparatus are

generally appreciated less readily than the qualitative, and this

was particularly the case in the seventeenth and eighteenthcenturies. The invention of instruments, therefore, did not have

that immediate effect of inducing greater rigour, and greaterinterest in refined measurement, which might be anticipated a


priori. The barometer, for example, was invented by Torricelli

in 1643. It was used originally to demonstrate the existence of

atmospheric pressure, and secondly as a means of exhausting a

small chamber formed at the top of the tube in which experimentscould be made. Only about 1660 was the correlation between

barometric pressure and climatic conditions discovered, and onlyafter this were attempts made to improve the readability of the

instrument and collect a "history of the weather." Later still,

Boyle employed the barometer as a gauge to measure the qualityof the vacuum formed by his air-pumps, and the amount of "air"

evolved from fermentations. The thermometer has an even longer,

and more surprising, history as a merely qualitative instrument.

The thermoscope, an instrument in which the expansion of air in

a bulb moved a column of water in a narrow tube upwards whenheat was applied, was invented by Galileo about 1600. Liquidthermometers were introduced about the middle of the century,and were extensively used by the Accademia del Cimento, but

none of these was calibrated. The first suggestions for systematiccalibration with the use oftwo fixed points were made about 1665;Fahrenheit's scale was devised about fifty years later, and the

modern centigrade scale only in 1743. Thus the first century of

thermometry yielded no quantitative measurements which can

now be interpreted with any degree of confidence. 1

While seventeenth-century astronomers, continuing a long

tradition, effected a refinement of angular measure which bore

fruit in Flamsteed's Historia Coelestis Britannica (1725), in physicsand biology qualitative results were far more significant. Even the

allied science of terrestrial angular measure (in surveying and

geodesy) remained rather crude until vernier scales and telescopic

sights were introduced at the close of the century. Consequentlyit can scarcely be maintained that technical limitations to accuracyof measurement were significant in any other branch of science

than astronomy before the early part of the eighteenth century.

Certainly it has been argued that chemistry would have pro-

gressed faster, and the science of heat have been more systematic,if greater attention had been paid to the quantitative aspects of

1 The tubes of the early thermometers were of course divided, so that

comparative readings could be taken, but without reference to any standardscale. Thus, extensive observations were rendered useless by the fact that theydepended on the arbitrary divisions of a unique instrument.


experiment; but the reasons for the neglect of these aspects are to

be sought rather in the nature of scientific activity in the seven-

teenth century, than in instrumental deficiencies. The importanceof accurate measurements was not adequately understood, ^andtherefore they were rarely made; so that it was the texture of

science that hindered the effective exploitation of devices alreadyin being, rather than vice versa.

On the other hand, with regard to the two qualitative instru-

ments which most strikingly opened up great new fields of activity,the telescope and microscope, it is plain that technical limitations

rapidly became serious, and that the nature of these limitations

was well understood. Both instruments began in very crude form.

Systems of convex lenses replaced the concave-convex combina-

tion (the so-called Galilean arrangement) only gradually fromabout 1640, when rules for working out the appropriate focal

lengths and apertures were better understood. The first true com-

pound microscopes date from about this period, and the new

(Keplerian) telescope brought more detail of the solar system into

visibility. Additional satellites were discovered; the mysterious

appearance of Saturn was accounted for; transits and occultations

could be observed with higher accuracy. But the great desideratum

of seventeenth-century astronomy an observational proof of the

earth's rotation was not accomplished. To increase magnifica-tion without a corresponding vitiating increase of the aberrations

the astronomer was compelled to use very long focal lengths andsmall apertures. The light-gathering power of such instruments

was poor, and a practical limit to length (about 100 feet) was soon

reached. Non-spherical curvatures for lenses were theoretically

desirable, but technically impracticable. Newton's optical theory

explained the nature of chromatic aberration without suggestingan appropriate remedy, for he found that the separate colours

into which white light can be resolved could not be broughtto a single focus by a simple lens. The reflecting telescope, free

from chromatic aberration, was suggested by James Gregoryand first constructed by Newton, but it was hardly of serious

value to astronomers before the later years of the eighteenth

century.Similar problems were encountered in the microscope. Simple

glasses, with a magnification of about ten diameters, were used

early in the seventeenth century; by Harvey, who observed the


pulsation of the heart in insects, and by Francesco Stelluti who

published in 1625 a microscopic study of bees. The small tubular

"flea-glass," with the lens mounted at one end, and the object set

against a glass plate at the other, became popular among the

virtuosi. Towards the middle of the century the compound micro-

scope attracted renewed interest, being now constructed with a

bi-convex objective and eye-lens, with a plano-convex field lens

placed between to concentrate the rays. In the improved designof Hooke (described in Micrographia y 1665) the body, containingextensible draw-tubes, was mounted so that it could be tilted to a

convenient angle; a long nose-piece engaged in a large nut, so that

the body could be brought to focus on the object by screwing it in

or out. The lead-screw and slide method of adjustment was in-

vented later by Hevelius. To illuminate opaque objects Hookeused an oil-lamp and bull's-eye lenses; before the reflecting-

mirror was fitted (about 1720), transparent objects were examined

by placing a lamp or candle on the floor beneath the instrument,

which was often pierced through the base. The compound micro-

scope was complicated and expensive, but it was easy to handle,and in mechanical design became steadily more efficient. Opticallyit was less satisfactory. Magnifications exceeding 100 diameters

could be obtained, but the uncorrected lenses, made of poor glass,

gave low resolution. As a result, the point was soon reached where,

though the object could be made to appear larger, no finer detail

in it could be seen. From 1665 until about 1830, when satisfactory

corrected lenses became available, the compound microscopemade comparatively slight advance in optical properties. Thelimitation imposed, on biological research in particular, is obvious.

Nevertheless, the compound microscope was eminently a scien-

tific instrument, and Hooke's Micrographia the first treatise on

microscopy. Since his objects were fairly coarse (insects, seeds,

stones, fabrics, a razor's edge, leaves, wings, feathers, etc.), andsince he did not seek to penetrate into anatomical structure bydissection (though he examined the compound insect eye, anddiscovered the cellular composition ofcork) he was able to producea series of admirable illustrations despite the limitations of his

microscope. Most of the discoveries of the time in minute ana-

tomy, associated with the names of Malpighi, Swammerdam and

Grew, such as the capillary circulation of the blood, could also be


demonstrated with the compound instrument. 1 For the very finest

observations, however, another technique was required, in which

the Dutch microscopist Antoni van Leeuwenhoek excelled. The

compound microscope had stimulated the grinding of very small

bi-convex lenses of short focal length for use as objectives. It was

found that better results could be obtained by mounting such high-

power lenses, or even tiny fused glass spheres, as simple micro-

scopes than by using them as elements in an optical system that

multiplied the aberrations. For considerable magnification the

lenses had to be less than one-tenth of an inch in diameter; theywere proportionately difficult to grind and manipulate, and they

imposed severe eye-strain. But Leeuwenhoek reported, in his

letters to the Royal Society, observations obtained by this meanswhich were only repeated with the achromatic microscopes of the

nineteenth century. His skill as an optician is further shown by the

fact that one of his few surviving lenses has been proved, by recent

tests, far superior to any other known simple lens; others of his

own make are good but not outstanding. This skill enabled him to

study more thoroughly than any other observer spermatozoa andthe red corpuscles in the blood and to become the first to discern

protozoa and bacteria. Despite some contemporary incredulity,

aroused by the great number and disparity of Leeuwenhoek's

original discoveries, and the difficulty of confirming them, his

work was astonishingly accurate. He was also creditably free from

the tendency to theorize, or to allow his imagination to play with

his microscopic images. At the end of the century Leeuwenhoekwas alone in his investigation of microscopic creatures, althoughothers were engaged on the study of the microscopic parts of

larger creatures; his results, therefore, remained largely isolated

curiosities. In the eighteenth century the description of various

animals, visible to the naked eye but capable of being studied onlywith the aid of the microscope, was taken up both in England(Baker, Ellis) and in France (Reaumur, Bonnet, Lyonet). Tremb-

ley, whose monograph on the hydra has become a classic, workedin Holland and was closely associated with both the English andthe French groups of naturalists. All these worked with the simple

microscope but at a much lower magnification than that frequently

employed by Leeuwenhoek. This instrument thus became estab-

lished in familiar use among zoologists and botanists for much the

1 See below, p. 286.


same purposes as it serves at the present time, when the higher-

powered compound microscope, given a beautiful mechanical

construction by the English instrument-makers, was still of little

scientific value. The continuation of the sciences of histology and

cytology, begun by Malpighi and Leeuwenhoek, depended uponthe perfecting of lenses which proceeded swiftly in the early

nineteenth century.

It would be possible to develop other, comparable, instances

ofthe way in which, after an initial seventeenth-century invention,

a long interval followed before, in a stage of higher proficiencyin instrumental techniques, observations or measurements of a

different order became practicable. The Newtonian reflecting

telescope, with HerscheTs improvements, for the first time enabled

the astronomer to escape the confines of the solar system. If the

"chemical revolution" of the eighteenth century was effected

without profound modifications of apparatus, on the other handthe chronology of electrical science was fixed by the discovery of

instruments for the creation, and the measurement, ofcharges andcurrents. These in turn induced new chemical techniques, such

as electrolysis. During that century a considerable literature grewup dealing with the manufacture and use of scientific instruments

of all kinds, and teaching the technique of making experimentsand observations, while the actual manufacturers strove intelli-

gently to improve their wares. John Dollond, the practical manwho solved the problem ofmaking achromatic telescope objectives

which had baffled mathematicians, was an instrument-maker.

The marine chronometer, in the perfecting of which so much was

due to another practical man, John Harrison, imposed a close

collaboration between watch-makers and astronomers. Science,

therefore, entered into a promising situation with the early nine-

teenth century, being able to call upon the services of a skilful

and progressive specialized craft, and realizing far more perti-

nently than hitherto its own dependence upon its material equip-ment. In nearly every respect its progress was involved in that of

some instrument, or in that of a variety of laboratory techniques.Because a three-fold division of function may exist in science,

between the instrument-maker, the laboratory worker and the

theorist, it has always been possible, and still is, for the strategic

thinking in science to take place outside the laboratory, away from


the instruments (though it may still be controlled by the accessible

mathematical techniques). Thus Tycho's instruments were made

by the metal-workers of Augsburg; he himself managed their use

with consummate skill; and his results were interpreted by the

mathematician Kepler. But the third function without the second,and the second without the first, can clearly yield only diminishingreturns. The progress of science demands originality at all three

levels; more than this, it may demand the existence of resources

of industrial magnitude, of a glass-industry, a gas-industry, of the

great plants required to produce antibiotics and radio-active iso-

topes. If it seems increasingly likely that the major advances of

the future will come from large institutes, freely endowed, and as

the result of co-operative labours, it is no more than a fresh stepin that growth of complexity, and of an increasing reliance on

techniques and tools of investigation, which was typical of the

scientific revolution. In a sense it is the fulfilment of Bacon's

foresight.

CHAPTER IX

THE PRINCIPATE OF NEWTON

Emight be misleading to suggest that the career of Isaac

Jewton represents the peak of the scientific revolution, the

,oint at which the transition from renaissance to modern

science became complete. The qualifications to be added to such

a generalization are obvious. Profound changes in the methods

and theories of the non-mathematical sciences, upon which the

impact of Newton was negligible, were deferred to future times.

He showed no interest in biology; perhaps, indeed, to his highly

organized intellect its structure was wholly alien. It could be

argued that Newton's essentially physical approach to chemistrywas no less a departure from the traditions of that science than

Lavoisier's theory of chemical combination, but Newton's ideas,

despite their surviving historical interest, proved unconstructive.

Their ingenuity was premature, and Newton, like Boyle, in his

treatment of chemistry as a branch of corpuscular physics more

nearly resembled an ancient philosopher than a nineteenth-

century chemist. The clear light shining through his mathematical

and physical researches did not illumine other, darker quarters of

Newton's mind and character. The author of the Principia wasalso the compiler of millions of words of extracts from the most

obscure alchemical writers; the great mathematician laboriously

computed the generations that had passed since the creation of the

world. Despite his genius, despite his rapid and sure mathematical

invention, despite his experimental precision, science was alwaysfor Newton a detached intellectual pursuit, not an activity, a

cause, close to the emotional core of his being. Strangely, to

modern ways of thinking, alchemy seems to have given him a

greater sense of the ultimate mystery than his unfolding of the

celestial system. To many of the critical issues of the scientific

revolution he was insensitive. Unlike Descartes or Boyle he felt

impelled to utter no fundamental pronouncements on the trinity

of God, Nature and Man. Cutting neatly and narrowly throughthe froth swelling up from the intellectual ferment of his age,

withdrawing himself from idealists and propagandists, the social,

244

THE PRINCIPATE OF NEWTON 245

religious and philosophic implications of the scientific revolution

scarcely touched him. Newton saw the ideal of scientific truth se-

renely, as an end attainable by the application of methodical prin-

ciples; it provoked in him no warm revulsion against established

errors, no enthusiasm for a hopeful shift in the course ofcivilization.

Even Newton, therefore, cannot be described without reserva-

tion as a" modern scientist." His own attitude to nature still bore

traces of the medieval; he faced some problems which the modernworld considers unworthy of serious consideration, and by con-

trast philosophized sometimes in such a fashion as to gloss over

other problems which have since become important. Nevertheless,

Newton's contributions to those branches of physical science that

were studied in the seventeenth century mark a peak of achieve-

ment. At the same time they disclosed fruitful prospects for the

future advance of science, but where the influence of Newton wasmost profound in the theory of gravitation, in the theory of

light, and in the particulate theory of matter his own examplewas so commanding, and his own explorations were ofsuch range,that for about a century no investigation passed the limits of the

Newtonian framework. [Newton may be pictured as establishing

developing sciences at a nfew level, less by seeing the problems in

ways unimagined by his contemporarig^lhan by the exercise of

his greater ability and mathematical skill.V\t about this level theyremained until the nineteenth century^was well advanced, while

the major creative impulse was transferred to the less organized

departments of science, to chemistry and biology, and in physicsto the study of heat and electricity. The comparative stagnation in

the eighteenth century of those aspects of physics which had seen

most revolutionary developments in the seventeenth is a measure

of Newton's success in extracting the quintessence of knowledgefrom those scientific procedures which the seventeenth century had

developed most highly; for long it seemed that in those aspectsno other procedures, and no greater knowledge, were possible.

The Newtonian theory of light was severely shaken by Youngand Fresnel about 1820, and at the same time a notion of electrical

attraction among the ultimate particles of matter was gradually

replacing the Newtonian idea of a gravitational attraction. These

were the first checks to the established structure of physics, while

serious doubts of the inviolability of Newtonian or classical

mechanics only arose at the very end of the nineteenth century.


Throughout a long period of more than 150 years Newton's

scientific thinking in mathematical science appeared practically

infallible; other aspects of his intellect were still almost completely

hidden, partly owing to the caution of his literary executors and

editors, who carefully marked so many of his manuscripts as

"Not fit to be printed," partly owing to Newton's own reticence in

publication.1 Before 1684 Newton was a comparatively unknown

professor of mathematics in the University of Cambridge; his

optical experiments and construction of a reflecting telescope,

with his mathematical discoveries which were known only to a

limited circle, had given him a certain repute, but he had wonno striking acclaim. The publication of the Mathematical Principles

of Natural Philosophy in 1687 immediately gave him enormous

prestige. The Royal Society recognized something of its majestyeven before the book was printed; foreigners, though more reluc-

tant to accept Newton's theories, were quick to perceive the geniuswhich had given them a mathematical dress. The tone was set byEdmond Halley's opening ode to the volume whose publicationhe generously undertook :

. . . Talia monstrantem mecum celebrate camaenis,Vos o caelicolum gaudentes nectare vesci,

Newtonum clausi reserantem scrinia veri,

Newtonum Musis charum, cui pectore puroPhoebus adest, totoque incessit numine mentem;Nee fas est propius mortali attingere divos. 2

A somewhat fulsome adulation was maintained by English writers

to recent times (e.g. in Brewster's Life of Newton, 1855); others

were more critical in equally sincere admiration. Even today the

distinction between that which was of permanent value in

Newton's scientific thinking, and that which was stamped with

the character and preconceptions of his age, is not always very

clearly indicated. The fact is (as might be expected) that in their

manifold and complex aspects Newton's contributions even to

1 Most of his works appearing in his life-time, other than the Principia, the

papers in the Philosophical Transactions, and the Opticks (delayed until after

Hooke's death), were first printed without his consent.1 *O you heavenly ones who make merry on nectar, celebrate with me in

song the revealer of these things, Newton to the Muses dear, Newton whounlocked the barred treasure-chest ofTruth: Phoebus is in his pure breast, andenters his mind with all his own divinity. Nearer the Gods no mortal mayapproach.

9


mathematics and mathematical science were not all equally useful,

though all were important. Newtonian mechanics, and his

celestial system, have stood firm within limits which are now

clearly defined; but of the remainder of Newtonian science the

last century has left scarcely a vestige.

Clearly Newton, like most great men, was fortunate in the hour

of his birth: in 1642, the year of Galileo's death. His adolescence

was accompanied by the foundation of scientific societies, the

practice of systematic experiment, the gestation of modern mathe-

matics. In 1665-6 the rather unpromising, and certainly ill-

grounded student upon whom Barrow had enforced the study of

Euclid's Elements was in the "prime of his age for invention."

How much the fruit of his originality owed to the ground from

which it sprang, to Barrow, to Wallis, Slusius, Kepler, Borelli,

More, Boyle, Descartes and others whom he read in those early

Cambridge years!1 How many, and how rich, were the threads

which these giants led to the hand of so able a spinner of theorems,so close a weaver of theories! The genius that was frustrated by the

dense mysteries of chemistry reaped a splendid harvest in the

riper fields of mathematical science in which its fullest powerscould be exercised. It is no detraction from Newton's originality

to point out that all his discoveries were firmly rooted in the science

of the time that like a helmsman he was borne along by the

stream that eiach of them has a quality of inevitability in its

contemporary context. Newton, in fact, won such immediate

esteem because he saw clearly the things to which others were

groping, because he was so fully in harmony with his age. Notscientists and mathematicians alone, but philosophers and theo-

logians could find in Newton exactly that of which they wished to

be assured. Even in his political allegiance to a limited Protestant

monarchy, in his ambition to rise in the great world of affairs,

and in his shrewd financial sense, Newton was a good and success-

ful citizen of Augustan England, a bon bourgeois when the middle

classes were rising to luxury and power.

There are no singularities in Newton's early years. As a student

in Cambridge, he was fashionably inclined to scepticism of the

1 One would naturally like to add the name of Galileo to this list, but thereseems to be no evidence that Newton met Galileo in the original, at least at

this time.


Cartesian system, looked favourably upon hypotheses of atoms

or corpuscles, and developed a mild academic interest in the

empirical method represented by Boyle. Starting rather late, he

rapidly assimilated the latest mathematical knowledge, but

although his notebooks show him at the age of twenty-three

already deeply interested in science, they contain no sketch of

an original contribution, no hint of a sudden revelation of the

importance of natural knowledge. He was always apt, much later

in life, to regard science as an importunate mistress, to work with

immense concentration and speed upon a problem when the

passion to solve it fell upon him, because a part of himselfdoubted

the problem's cosmic significance. Then, for the better part of

two years after he had taken his degree, Newton was forced into

retirement at his country home in Lincolnshire by the plaguewhich raged in the towns and villages during 1665 and 1666. Hehad already begun his optical experiments (which seem to have

been prompted by undirected curiosity, rather than by any

clearly perceived ambition), and his mind was turning towards

new conceptions in mathematics. In the winter of 1664-5 he hadfound the method of infinite series, and shortly after discovered the

binomial theorem; in Lincolnshire during the following summerhe calculated a hyperbolic area to fifty-two places of decimals;in November of the same year he had formulated the direct

method of fluxions (differentiation), and in May 1666 he began

upon the inverse method (integration). During the whole of 1665he must have been working at his optical experiments, and tryingto grind lenses of non-spherical curvature, and early in 1 666 he

"had the Theory of Colours." This quickly directed him to the

construction of his first reflecting telescope. 'And the same year/wrote Newton long afterwards, 'I began to think of Gravity

extending to y6 orb of the Moon, & (having found out how to

estimate the force with which a globe revolving within a sphere

presses the surface of the sphere), from Kepler's rule ... I deducedthat the forces which keep the Planets in their Orbs must [be]

reciprocally as the squares of their distances from the centers

about which they revolve.' To this period belongs the famous

story of Newton and the Apple, told at first hand by Newton's

younger friend, William Stukeley:

After dinner, the weather being warm [the date was 15 April 1726],we went into the garden and drank thea, under the shade of some

THE PRINGIPATE OF NEWTON 249

applctrees, only he and myself. Amidst other discourse, he told me,he was just in the same situation, as when formerly, the notion of

gravitation came into his mind. It was occasioned by the fall of an

apple, as he sat in a contemplative mood. Why should that apple

always descend perpendicularly to the ground, thought he to himself.

Why should it not go sideways or upwards, but constantly to the

earths centre? Assuredly, the reason is, that the earth draws it. Theremust be a drawing power in matter: and the sum of the drawingpower must be in the earths center, not in any side of the earth.

Therefore does this apple fall perpendicularly, or towards the center.

If matter thus draws matter, it must be in proportion of its quantity.Therefore the apple draws the earth, as well as the earth draws the

apple. That there is a power, like that we here call gravity, whichextends itself thro the universe. 1

When the plague had subsided, Newton returned to Cambridge,

presumably in the hope (which was soon fulfilled) of becoming a

Fellow of Trinity College; in 1669 he succeeded Isaac Barrow in

the Lucasian Professorship of Mathematics. He was now com-

fortably established in a life that was to be his for nearly thirty

years. Professorial pupils were few, though Newton must have

done some college teaching; he had ample leisure for his experi-

ments in optics and chemistry, and for his mathematics. In 1672letters written to Oldenburg, describing the new theory of colours,

brought him into the Royal Society but the disputes and criticisms

which followed during the next four years (aggravated by the

officiousness of Oldenburg) persuaded Newton virtually to cut off

this connection. His interest in alchemy and chemistry quickened;the wooden staircase leading from his first-floor rooms to the

furnace in the little garden below was shaken by his eager tread.

It was Halley who brought Newton back into the scientific move-

ment, who encouraged his interest in mathematical matters, andwas the godfather of the Principia. The book was begun towards

the end of 1684, and was finished by the spring of 1686. Thereafter

Newton's life became more full of incident, and more empty of

science. He took part in the resistance to the Catholic policy of

James II; sat (silently) as a Member of Parliament; and sought

1 William Stukeley: Memoirs of Sir Isaac Newton's Life, ed. by A. HastingsWhite (London, 1936), pp. 19-20. Stukeleywas forty-five yearsjunior to Newton,who was in his eighty-third year in 1 726, and did not compose his memoir until

1752. His expressions, therefore, cannot be taken very strictly as interpretingNewton*s state of mind in 1 6656.


to become Provost of King's College.1 His fame, and his new

acquaintance with John Locke, made him known personally to

men who possessed political power and influence. The prospect of

exchanging academic seclusion in a provincial town for an office

of honour and profit in London was welcome. The initial frustra-

tion of this ambition, working in a mind intolerant of opposition at

a time when it was strained by overwork, caused a serious break-

down during 1693. After some months Newton recovered his full

intellectual powers, but it is to be doubted whether his judgementof men's actions ever regained a normal balance. 2 This illness

brought his creative scientific work to a close. Honours and fame

came later; in 1696 Newton left Cambridge to become first

Warden, then Master of the Royal Mint; in 1703 he was elected

to the Presidency of the Royal Society, which he held for the rest

of his life; in 1705 he was knighted. In the Augustan Age Newtonand Pope ruled the intellectual world with a sway more absolute

than that of the Queen herself.

That branch of science in which Newton had first published

original discoveries was also the last to be enriched by his mature

reflections. The bulk of the Opticks of 1 704 had long been written,

but the Queries with which the book concludes represent Newton's

final contribution to science, and perhaps the sum ofhis perceptionof nature. In the Queries optical phenomena are discussed in order

to throw light on the ultimate particulate structure of matter:

Have not the small Particles of Bodies certain Powers, Virtues, or

Forces, by which they act at a distance, not only upon the Rays of

Light for reflecting, refracting and inflecting them, but also uponone another for producing a great Part of the Phenomena of

Nature?8

1 Newton's extraordinary mastery of detailed argument is well revealed in

the legal briefs that he drew up for the royal benefit to confute the contentionsof the Fellows of King's. His claim brought him into touch with Christiaan

Huygens, whose brother Constantyn had come to England in the service ofWilliam III. It is pleasant to think of these two great, and very different,scientists setting off in a coach to petition their common sovereign to promoteNewton in the academic hierarchy.

1 Newton's mental illness was a definite paranoia, in which he accused his

closest friends of persecuting and calumniating him. Locke, in 1 705, privatelydescribed him as *a little too apt to raise in himself suspicions where there is noground'; this mental trait, which he always had, was played upon by men of

greater ambition than discretion in the quarrel with Leibniz, wherein Newtonlost all sense of proportion and probity.

8Opticks, Bk. III,Q.u.3i.


Newton, indeed, for the first time made optics a branch of physics,

by his demonstration that the theory of light and the theoryof matter were cognate and complementary. Before the mid-

seventeenth century the science of optics was almost wholly geo-

metrical, and it is interesting that progress was achieved throughrenewed attention to its qualitative aspects. Since the character-

istic colours of bodies and pigments had long been regarded as

true Aristotelean qualities, confusion followed upon the challengeto Aristotle's philosophy in the time of Galileo. The prismaticcolours also had long been familiar; in the middle ages an increas-

ingly more perfect account of the formation of the colours in the

rainbow had been given by the Latin writers who, following

Alhazen, regarded them as produced by the refraction of sunlightin shining through rain-drops. The geometrical optics of the rain-

bow were further perfected by Descartes, who also put forward a

new and more definite corpuscular hypothesis of light. In his view,

light was a sensation caused by pressure of the mattire subtile on the

optic nerve, set up by the tendency of this matter to expand in ail

directions from its concentration in the luminous source; colours

were caused by rotations of the particles of the matiere subtile.

This was, like all the science of the Principles of Philosophy, an

unsupported hypothesis. Descartes assumed that light travels

more rapidly in a dense medium (such as water) than in air, andfrom this the sine-law ofrefraction could be deduced; but the samelaw could also be deduced from the contrary assumption. There

was no method of proving either by experiment. The explanationof what happens to "light" itself when a beam of white light is

converted into a beam of one or more colours was vague and

wholly speculative. In all theories before Newton's, a qualitative

change in the nature of the beam was suggested, a modification

of the physical entity of light, which at least in imagination could

be reversed, so that as red light can be derived from white, white

ought to be derivable from red. The same potential reversibility

is implicit in the more ingenious theory of colours described byRobert Hooke in Micrographia (1665). Hooke was the first investi-

gator of the colours produced by optical interference in the form

known, somewhat unjustly, as "Newton's rings," which he ob-

served in the laminations of mica, and in plates of glass pressed

together, finding that the manifestation of the colours dependedupon the existence of a very thin refracting medium, each colour


corresponding to a determinate thickness. According to Hooke,the sensation of light is caused by a very rapid, short vibrating

motion in the transmitting medium, every pulse or vibration of

the luminous body generating a sphere 'which will continually

increase and grow bigger, just after the same manner (though in-

definitely swifter) as the waves or rings on the surface of the water

do swell into bigger and bigger circles about a point of it, where,

by the sinking of a stone the motion was begun.' Therefore, each

successive pulse or vibration may be considered as being at right

v\ AIR

(less easy transmission)

WATER(more easy transmission)

FIG. 8. Hooke's Theory of Refraction.

aaabbby incident ray; cccddd, refracted

ray. ab, ab perpendicular pulses, cd,cd oblique pulses.

angles to the direction of pro-

pagation radially from the

centre, and in a narrow beamof light each pulse as a planesurface perpendicular to the

beam. 1

Hooke next investigated

geometrically the results ofthe

passage of the beam from one

medium into a second which

is capable of transmitting the

pulses more, or less, easily than

the first. He reasoned that if

the light falls obliquely uponthe surface separating the two

media, one "edge" of the

pulse (treated as a plane)would enter the second medium before the other, and wouldtherefore be accelerated or retarded before the latter, in turn, hadstarted to travel through the second medium (Fig. 8) . He assumed

(without proof) that when the second medium transmitted the

pulses more easily the beam would be refracted towards the per-

pendicular, and consequently that water transmits more easilythan air. 2 This refracted ray, moreover, would be distinguishedfrom the incident ray in that the pulses would now be oblique,

1Micrographia, pp. 55-7.

* In this Hooke followed Descartes. Fermat had already demonstrated thatrefraction towards the perpendicular occurs when the velocity of light in thesecond medium is less, i.e. when like water or glass it transmits light less easilybecause it is more dense than air. Huygens, in the Traiti de la Lumiere (1690)wherein he follows Fermat, by introducing the conception of the wave-frontinto the pulse-theory showed that the sine-law of refraction followed from it.


not perpendicular to the ray, due to the acceleration or retarda-

tion of the "leading edge" of each pulse.1 To this obliquity of the

pulse Hooke traced the sensation of colour, on the grounds that in

a whole beam oflight there would be some confusion ofthe oblique

pulses, and that one "edge" of each pulse would be weakened or

blunted through having to initiate the vibration in a medium at

rest; thus:

Blue is an impression on the Retina of an oblique and confus'd pulseof light whose weakest part precedes, and whose strongest follows.

Red is an impression on the Retina of an oblique and confus'd pulseof light, whose strongest part precedes, and whose weakest follows.

For example, in Fig. 9, towards a the leading edge of each oblique

pulse, being adjacent to the un-

disturbed medium, is weakened,whereas towards d the lagging

edge pulse is weakened for the

same reason. Hence the colour

blue will be seen about a, and red

about d. Hooke thought that

the intermediate colours of the

spectrum 'arise from the com-

position and dilutings of these

two '

produced by the confusion _ TT , , ^L ,

r .1 . . . f FIG. 9. Hooke s Theory of Colours,of the two primary types of

oblique pulse towards the middle of the refracted beam. Hefurther showed by a very ingenious analysis that when a raypasses through a very thin medium a similar succession of strong-weak or weak-strong pulses is created, according to its thickness,

producing colours.

In this theory of light, Hooke devised a subtle mechanism bywhich colours might be derived from white light considered as atrain of uniform and homogeneous pulses. It accounted for the

association of heat, light and motion in a crudely sketched kinetic

theory; for the fact that refraction is always accompanied bycoloration; for the order of the colours as produced by refraction

or by interference; and for the fact that the spectrum produced byone prism can be re-converted into white light by a second. On

1Huygens (see note 2, above) avoided this supposition of obliquity by

different reasoning on the formation of the refracted wave-front.


the other hand, it was not very clearly conceived in detail, and it

explained only a selection of the known facts. Hooke seems to

have observed that the two sides of a refracted ray are not parallel,

but makes no mention of the fact (cf. Fig. g).1Probably no experi-

ments on homogeneous coloured light were made by him, since

he seems not to have known that further refractions have no effect

upon such light; this would certainly have been difficult to recon-

cile with his theory. The most serious objection against its broad

form was that it failed to account for the rectilinear propagationoflight. If a ray was a train of pulses, why did not these spread out

into the surrounding medium, as sound-waves do? This was, in-

deed, for long a profound objection against any pulse or undula-

tory theory, having been thoroughly discussed by Newton in the

Opticks.

So far the theory of light had been illuminated by few new

experiments, and none that were decisive. The ideas of Descartes

and of Hooke could have been as well propounded in the four-

teenth century as in the seventeenth. The new experimental evi-

dence, relating to interference (Hooke) and diffraction (Grimaldi,also 1665) seemed to favour the pulse hypothesis, but though the

two opposed theories were equally mechanical in character, theywere nevertheless ad hoc hypotheses, entirely lacking in the demon-strative solidity on which the "new philosophy" was supposed to

be founded. By introducing imaginary mechanical qualities of

pellucid matter, the old Aristotelean theory of colour as a qualityhad only been pushed back to a further remove. Newton's experi-ments began where the theories of Descartes and Hooke, with

which he must certainly have been acquainted, ceased in new

experiments. His papers in the Philosophical Transactions, containinghis new theory of prismatic colours, are hardly more than the

statement of experimental results. The deductions he drew were

simply those enforced by the new evidence.

His first paper begins with the observation that a parallel beamof white light diverges into the spectrum when it is refracted bya prism. The spectrum is longer in one direction, not of the same

shape as the aperture through which light is admitted. This musthave been noticed often, and disregarded. Both in the Opticks,

and in his note-book, however, Newton first describes another

1 This is shown in Fig. 2 of Schem. VI of Micrographia, where, however, theincident ray is shown as convergent though Hooke purports to be using sunlight.


experiment, in which he observed a continuous line, painted in

two colours, through the prism and found that the image of the

parti-coloured line was no longer rectilinear. Perhaps this gave himthe first clue to what followed. These simple experiments taughtNewton that 'y

crays which make blew are refracted more y

ny*

rays which make red,'1 or as he phrased it after many more ex-

periments described in the Opticks, 'the Sun's light is an hetero-

geneous Mixture of Rays, some of which are constantly more

refrangible than others.' Any refracting agent, such as a prism,

simply acted like a filter to distinguish the infinite components of

white light according to their refrangibility. Therefore, he thought,it was necessary to give up all hope of contriving a lens whichwould refract all colours equally, and so yield an achromatic

image. Newton was careful to prove that monochromatic light has

all the optical properties that were "vulgarly" attributed to white

light, and that there could be no question of the white ray being

actually shattered by refraction it was merely divided, and it

could be reassembled. Each pure coloured constituent, however,was homogeneous and indivisible.

This doctrine appeared very shocking to contemporaries. The

simple nature of white light had always been accepted as axio-

matic. The proof that all the colours of the spectrum are equally

primary and necessary in white light cut directly across notions

which supposed them the product of mixtures of red and blue, or

blue and yellow. While some theorists of empiricism welcomedNewton's Baconian use of experiment, many who prided them-

selves on their knowledge of optics were hostile. The reactions of

the critics, Hooke and Huygens amongst them, are interesting.

When Newton's first paper appeared in the Philosophical Transac-

tions, they judged initially that he was merely speculating, andtried to answer with irrelevant arguments. Then they denied that

the experiments gave the results described by Newton, or main-

tained that if the experiments were correct the conclusions drawnfrom them were false. Finally, it was alleged that if Newton's ideas

were justifiable, they were not original. Neglecting the minor

critics, it may be doubted whether either Hooke or Huygenstwo of the leaders of the scientific movement ever succeeded

entirely in adjusting their thinking in accordance with the evidence

1Cambridge MS. Add. 3996: cf. the author's note in Cambridge Historical

Journal, vol. IX (i948) PP- 239-50.


of Newton's experiments. The former never understood that his

own pulse-theory could not account for them. The latter, in his

Traiti de la Lumiere (1690), tactfully omitted the subject of colour

completely. Their failure is not more surprising than that of other

scientists in more recent periods who have equally resisted an

innovation which has inevitably overwhelmed their criticism.

Newton's propositions were revolutionary, not only in their con-

tent, but because they were founded straightforwardly on new

experimental evidence. It is, in one sense, an indication of the

superficiality of the change in spirit effected by the scientific revo-

lution that such obvious conclusions drawn from such easily

repeatable experiments should have been treated as matters for

argument. Empiricism that is, in this instance, Newton's reti-

cence in his original papers on the question of what light is, and

the reasons for the properties exhibited by a lens or prism was

still obstructed by the inertia of established theory, which could

prevent an accurate factual description being estimated at its true

worth. In another sense, the dispute carried on in the pages of the

Philosophical Transactions was the product of a confusion between

facts and their interpretation which is perhaps inevitable in

science at its growing point. Of this there are many examples, in

the incredulity with which Lavoisier, Darwin, Joule or Pasteur

was heard. Major scientific advances have not been made simply

by uttering the statement that, in certain conditions, "The red

line is higher than the blue," or "the thermometer reading was #."Newton did not make such a purely descriptive statement, for he

added that the red was higher than the blue because the constituent

coloured rays of white light are not equally refrangible. If un-

comfortable experiments have stuck in the throats of those weddedto established ideas, it is owing to their indissoluble connection

with a heterodox theory. In such circumstances, the new theo-

retical attitude may seem to leave incomprehensible more than

it seeks to explain, and then the question arises: "Is it worthwhile to alter the balance which is already struck between the

mysteriousness of nature and human understanding?"The most important of Newton's discoveries, because they were

most unconventional, aroused in many of his contemporaries the

feeling that the accepted conception ofnatural processes was being

wantonly disturbed in order to account for phenomena that

could equally well be treated without such intellectual upheavals.


It is, in the last resort, the function of cumulative experiment andobservation to prove that such supposed alternatives in explana-tion are unreal; triumphantly to defend the old, or vindicate the

new. In the course of the scientific revolution, the dominantantithesis had been between old and new methods and ideas,

broadly divisions among the" moderns" were trivial. Towards the

end of the seventeenth century this antithesis was becoming lifeless,

and other divisions between the moderns themselves became far

more critical. The appeal to experiment and observation had

played a useful part in resolving the former antithesis, but the

appeal to a new conception of what science should be, to a new

image of nature, to a new mathematics and structure of reasoning,in short to a new appraisal of familiar facts, had achieved far

more sweeping results. In many ways, genuine observation and

experiment had been the pivots of seventeenth-century biologyfar more than they had been of its mechanics and physics. Withthe empiricist reaction against Cartesian science, which hadseemed for a moment almost to sum up the whole revolt against

tradition, and especially with the discoveries of Newton, came the

test of the ability of the heirs of Copernicus and Galileo to resolve

their own internal contradictions. If these were not in turn to lead

to endless debate, such as had embroiled the heirs of Aristotle, it

could only be by a more rigorous attention to the criteria of

experiment. The fundamental significance of Newton's scientific

method was that it achieved this exactly; it did not show merelythat a theory roughly agreed with a selected group of facts, but

that a group however limited and restricted of theoretical

propositions could be associated with a range of experimental

facts, carefully checked and often repeated. Confidence could be

granted to such a group of propositions because it was unique,and the minimum necessary; because it claimed only to compre-hend a limited range ofphenomena that had been exactly studied,

and not to extrapolate from a few particulars to universal truths.

Against such a method the kind of criticism directed towards

Newton's theory of colour was unavailing in the long run; as was

that directed against Lavoisier orJoule. If, with regard to Newton,

expressions of incredulity were less well founded, it was perhapsbecause his precise use of the experimental method was not yet

understood.

Of course Newton did not restrict himself entirely to such


theoretical propositions as were firmly based on experiment. Toomuch has been made of his celebrated obiter dictum,

"I do not frame

hypotheses."Scattered through his works, and more freely through

his unpublished papers, are numerous comments suggestive of a

deeper penetration into the mysteriousness of nature than exact

science could yet achieve. Newton framed many hypotheses

which, he was inclined to think, might account for natural

phenomena, like gravitation or refraction, hardly as yet illumi-

nated by experimental inquiry; but he was always careful to

distinguish between such hypotheses and an experimentallyestablished theory. With him this distinction totally ignored byDescartes becomes fully self-conscious; hence the form of the

Queries in the Opticks. In these Queries Newton sketched out an

interlocking but not wholly consistent body of ideas relating to

the nature of light and matter which he regarded as possible, or

probable, but unproven. The most influential portions of this

discussion were those in which Newton considered the relative

merits of the undulatory (or pulse) and the corpuscular theories

of light. He has been generally regarded, with some truth, as the

classical advocate of the latter. But he was not wholly decided.

For example, in Query 13 the suggestion is made that the colour

of a ray depends upon the "bigness" of its vibration, the shortest

vibrations corresponding to violet, and the largest to red, just as

the pitch of sound corresponds to the "bigness" of the vibration

in the medium. 1Again, in Query 16, Newton asks, 'considering

the lastingness of the Motions excited in the bottom of the Eye byLight, are they not of a vibrating nature?

'

;and in Query 1 7 he

suggests that when a ray of light is reflected or refracted, vibrations

are set up in the medium which, radiating from the point of

incidence, 'overtake the Rays of Light, and by overtaking them

successively, do they not put them into the Fits of easy Reflexion

and easy Transmission described above?' As for the medium whose

vibrations should transmit light, Newton could conceive of an

aether, less dense than air but far more elastic, pervading all bodies

and expanded throughout the universe, transmitting heat by its

vibrations as well as light,2acting as the agent of reflection and

1 Newton's terminology is obscure: it is not quite clear whether by "bigness"he means amplitude or wave-length.

1 The existence of invisible (infra-red) heat rays was first demonstrated bySir William Herschel (1800).


refraction. Conversely, in Query 29 Newton declares: 'Are not

the Rays of Light very small Bodies emitted from shining Sub-

stances? For such Bodies will pass through uniform Mediums in

right Lines without bending into the Shadow, which is the Nature

of Rays of Light.5

Colour might be accounted for by supposing that the smallest

corpuscles of light gave the sensation violet, and the largest, beingless refracted, the sensation red. From his study of the double

refraction in Icelandic spar (which Huygens, in his Traitt de la

Lumiere, had failed to explain completely in terms of the wave-

theory) Newton concluded that the "sides" of a ray of light

might have different properties, and he did not see how these

could be associated with wave-propagation. These two points

were, for him, decisive objections against the ideas of Hooke and

Huygens, yet he himself found it necessary to conceive of a

periodicity in the "Fits of Easy Reflection and Transmission"

which he introduced in Book II in order to deal with the pheno-mena now ascribed to optical interference. 1 Newton's corpuscular

theory, therefore, did not render an aether unnecessary, nor did it

dispense entirely with the concept of aetherial vibrations. As he

was evidently not satisfied with its completeness, it was unfortu-

nate that some later physicists paid insufficient attention to

Newton's caution: 'Since I have not finish'd this part of myDesign, I shall conclude with proposing only some Queries, in

order to a farther search to be made by others.'

Not only does the Principia differ from the Opticks in form a

mathematical, as compared with an experimental, treatise but

its relationship to the contemporary scientific background is

different also. It presented no less of a puzzle to contemporariesthan the optical discoveries of fifteen years earlier, partly for the

same reason that Newton chose to propound even apparentlyabsurd theories if they alone suited the facts described, partly for

the additional reason that the propositions of the Principia seemed

to contravene the mechanistic philosophy which science had so

1 In each regularly successive "Fit of Easy Reflection*' the ray tended to bereflected upon meeting a surface; in between in the "Fits ofEasy Transmission"to penetrate into it. Thus the behaviour of a ray encountering the two surfaces

of a thin medium (such as the air gap between two glass plates) dependedupon the dimensions of the intervals between the surfaces and of the intervals

between the "Fits."


recently adopted with confidence. The theory ofgravitation stated

in terms of action at a distance was regarded by Cartesians as

no better than a revival of the occult forces from which science

had been liberated by mechanical hypotheses. Nevertheless, the

Principia was far more in keeping with a certain scientific tradition

one overshadowed by the triumph of Cartesian science than

was the Opticks; its thesis was more clearly anticipated in earlier

notions, due to Gilbert, Kepler, Borelli and Hooke; its materials

had largely been prepared by other hands than those of Newtonhimself.

Descartes had flatly denied the validity of attraction as a

scientific concept. Since all forces were mechanical in his view, a

body could move only because other bodies impacted upon it,

and so impelled it by pushing. Therefore he had described prob-able ways in which gravitational, magnetic, or electric

"attrac-

tions" might be caused by such impacts of the matiere subtile uponsolid bodies. His system implied that the various motions of the

planets around the sun were conditioned by the structure of

the solar system as a whole, and particularly by the propertiesof the aetherial matter, rotating like a vortex, with which it was

filled. They were not determined by separate relations between

the individual celestial bodies; this perhaps explains why Kepler's

empirical laws of planetary motion were of little interest to him.

The earlier notions of attraction, however, had conceived rather

of each celestial body, regarded as a physical entity, exerting aninfluence directly upon cognate matter. In Aristotle's theory of

gravity and levity the matter of the universe was drawn, or

attracted, to its natural place, the attraction being specific to

each kind of matter, since earth could not tend naturally to the

place of fire, nor vice versa. Thus the same kind of matter tended

to collect together in the same place. In the Copernican system,this concept of attraction to specific spherical layers about the

centre ofthe universe no longer had meaning, but the cosmic order

could be preserved by transferring the attraction from the placeto the matter which had, in Aristotle's cosmology, occupied that

place. The basic principle that matter tends to coalesce with like

matter implied by Ajistotle, could now emerge more clearly.

For Gilbert this principle, justified quite naively by teleological

reasoning, enabled bodies to preserve their integrity.*Cohesion

of parts, and aggregation of matter, exist in the Sun, in the Moon,


in the planets, in the fixed stars/ so that in all these bodies the

parts tend to unite with the whole 'with which they connect

themselves with the same appetence as terrestrial things, which wecall heavy, with the Earth.' 1 This means that gravitation is a

universal property of matter, but peculiar to each body; the same

gravity is not common to all, in Gilbert's view, because a piece of

lunar matter would always tend towards the moon, and never

adhere to the earth.

It might seem that after Galileo's contention that the rnatter of

earth, moon and planets the non-luminous heavenly bodies

was of the same kind, it would have been a straightforward stepto argue that all this earthy matter shared a common attraction,

like drawing like. But against such an argument the teleological

framework of the theory of attraction which was in no wayrequired to explain the known behaviour of lunar or solar matter,

apart from its consistency was doubly effective. In the first place,if the matter of the moon, for example, were attracted towards

the earth, the theory would cease to explain the cohesion of the

parts of the moon. Secondly, a common gravitational attraction

would suggest that all the earthy matter in the universe wouldcollect in one mass and this was Aristotle's view, which Galileo

opposed. Thirdly, neither Galileo nor any of his contemporariesknew of any function which such a common attraction could be

supposed to fulfil. The theory of specific attractions remained far

more plausible.This theory had been used by Gilbert, and by Copernicus before

him, as an alternative to the Aristotelean causation of the motions

ofheavy terrestrial bodies. It was less a new cosmological principle,

than a new physical principle applied to cosmology. As such it is

also used by Kepler:

A mathematical point, whether it be the centre of the universe or not,

cannot move heavy bodies either effectively or objectively so that

they approach itself. ... It is impossible, that the form of a stone,

moving its mass [corpus], should seek a mathematical point or the

centre of the world, except with respect to the body in which that

point resides. . . . Gravity is a mutual corporeal affection between

cognate bodies towards their union or conjunction (ofwhich kind the

magnetic faculty is also), so that the Earth draws a stone much morethan the stone seeks the Earth. Supposing the Earth to be in the

1 On the Magnet, trans, by S. P. Thompson (London, 1900), pp. 219, 229.


centre of the Universe, heavy bodies would not be borne to the

centre of the Universe as such, but to the centre ofa cognate spherical

body, to wi< the Earth. And thus wherever the Earth is assumed to be

carried by it s animal faculty, heavy bodies will always tend towards it.l

So far Kepler has said nothing very new. He has repeated that

the concept of attraction of like to like can replace the Aristotelean

concept of matter being attracted to specific places, and he has

limited his use of this concept to heavy bodies cognate with the

earth. But he has stated, for the first time, that the attraction

is mutual (the analogy between gravity and magnetism, so fruit-

fully begun by Gilbert, is now being extended), and this point he

amplified further:

If two stones were placed close together in any place in the Universe

outside the sphere of the virtue of a third cognate body, they would

like two magnetic bodies come together at an intermediate point,

each moving such a distance towards the other, as the mass of the

other is in proportion to its own.

Here an original conception of the magnitude of the motion due

to gravitational attraction was introduced( -j-

=) ,

in which it

\aa m^lwas related to the ratio of the masses of the two bodies. Kepler,

therefore, began the investiture of the theory of attraction with a

definite dynamical form. Further, he postulated that the earth andthe moon were cognate matter, like the two stones:

If the Moon and the Earth were not retained, each in its orbit, bytheir animal or other equivalent forces, the Earth would ascend

towards the Moon one fifty-fourth part of the distance between them,and the Moon descend towards the Earth about fifty-three parts; and

they would therejoin together; assuming, however, that the substance

of each is of one and the same density.2

Kepler then went on to demonstrate, from the ebbing and

flowing of the tides, that this attractive force in the moon does

actually extend to the earth, pulling the waters of the seas towards

itself; much more likely was it that the far greater attractive force

of the earth would reach to the moon, and greatly beyond it, so

that no kind of earthy matter could escape from it.8

1 Astronomia Nova; GesammelU Wcrke, vol. Ill, pp. 24-5.2Assuming also that the diameter of the earth is about 3} (v/53) that of the

moon, which is a little too large.3 Loc. '/., pp. 25-7.


Clearly no one invented the theory of gravitational attraction;

it grew through many diverse stages. And clearly also the genesisof the theory of universal gravitation is found in Kepler. Newton's

hasty calculation of 1666, his later theory of the moon, and his

theory ofthe tides, are all embryonicaliy sketched in the Astronomia

Nova. But the attraction was still specific, applicable only to heavy,

earthy matter; Kepler himself did not go so far as to suppose that

the sun and planets were also mutually attracting masses, or that

the dynamical balance he indicated as retaining the earth andmoon in their orbits with respect to each other also preserved the

stability of the planetary orbits with respect to the sun. He failed,

as Copernicus, Gilbert and Galileo failed, to see the full power of

gravitational attraction as a cosmological concept.

Nevertheless, Kepler's idea that the satellite revolving round a

central body is maintained in its path by two forces, one of which

is an attraction towards the central body, although applied only to

the earth-moon system, holds the key to all that followed and to

the Principia itself. Galileo, like Copernicus, had believed the

planetary revolutions to be "natural," i.e. inertial; the celestial

bodies were subject to no forces. Kepler, however, believed that the

motive force of the universe resided in the sun which, rotating

upon its own axis,*

emits from itself through the extent of the

Universe an immaterial image [species] of its body, analogous to

the immaterial image [species] of its light, which image is itself

rotated also like a most swift whirlpool and carries round with

itself the bodies of the planets.'1 Each planet, moreover, was en-

dowed with its own "soul" which influenced its motions. 2 Such

notions confused the dynamical elements of the situation for

Kepler since the sun's force operated tangentially upon the

planet, he did not imagine that a centripetal force was necessaryto retain it in the orbit. In the singular case of the earth and moon,it was necessary for him to suppose that the "animal or other

equivalent force" of the moon was sufficient to overcome the

attraction towards the earth which would have distorted its path.This physical, attractive property of heavy matter could not as yet

be made the basis of the stability of the celestial system; rather it

was a disturbing feature which the cosmological properties of the

heavenly bodies had to overcome.

1 Loc. tit., p. 34.2 Cf. Harmonices Mundi (1619), Gesammelte Werkt, vol. VI, p. 264 et seq.


With Descartes the position was altogether reversed. He knew

that bodies in free motion move in straight lines. He knew that his

planets, swirled like Kepler's in a solar vortex, would if uncon-

strained travel in straight lines outside its limits. He knew, there-

fore, that some centripetal force must bend these straight lines

into the closed curves of the orbits. Rejecting Kepler's mysterious

attraction, he supposed this force to be provided by the varying

density of the solar vortex, which resisted the planets' natural

tendency to recede towards its periphery.After the publication of Descartes' Principia Philosophic (1644)

which for the first time applied the law of inertia systematically to

the planetary motions, the elements of the problem of universal

gravitation were completely assembled. The essential step was to

replace Descartes' conception of the nature of the centripetal

force required to hold the universe together by the Keplerian idea

of attraction, with the sun taken as the central body. Kepler's

problem could now be approached from a completely fresh aspect:

knowing that the moon must be, as it were, chained to the earth

to prevent it flying off into space, might not this bond be that

"corporeal affection between cognate bodies towards their union"

described by Kepler? Three men, all about the year 1665, formu-

lated this question in similar terms, and attempted to answer it:

Alphonso Borelli, Robert Hooke and Isaac Newton.

Borelli, who was a member of the Accademia del Cimento, tried

to find in Kepler's ideas the basis for a complete mathematico-

mechanical system of the universe. 1 He regarded the light-rays

radiating from the sun as levers pressing upon the planets, re-

volving because the sun revolved, and able to exert a pressurebecause they were themselves material emanations. He explainedthat the least force would impart some motion to the greatest mass,and that therefore (in the absence of resistance) the planets wouldmove with a speed proportionate to the force impressed.

2This,

like Kepler, he supposed to become more feeble as the distance

from the sun was greater, so that the outer planets would movemore slowly than the inner. Instructed by Descartes, Borelli knewthat under such circumstances a centripetal force was necessary to

1 Theories Mediceorum Planetarum ex causis physicis deduct* (Florence, 1666).* As Prof. Koyr has pointed out, Borelli has unwittingly formulated the

Aristotelean doctrine. Acceleration, not velocity, is proportional to force

applied: hence Borelli's planets could never maintain a uniform speed.


maintain the planets in their orbits, but he carefully avoided speak-

ing of this as an attraction since the word was banned from the

phraseology of mechanism. Nor did he identify this force with

that which in the earth is called gravity. Instead, he postulatedthat all satellites in the celestial machine had a natural tendencyor appetite to approach the central body about which they re-

volve thus the planets sought the sun an appetite constant at

all distances, and not at all affecting the central body itself. The

stability of the planet in its orbit was therefore conditioned by the

perfect balance of the centrifugal and centripetal forces to which

it was subject, and this he was able to illustrate experimentally;but Borelli was further required to explain why these orbits are

elliptical, not circular. The answer is highly ingenious: Borelli

imagined that each planet was created outside its circular orbit.

In this position the excess of centripetal over centrifugal force

would urge the planet to its proper distance from the sun, but the

momentum acquired would carry it beyond, to a point inside the

circular orbit. Here the centrifugal would exceed the centripetal

force, and the planet would again be pressed outwards, and againcarried by momentum to its former station. 1 Then the cycle wouldbe repeated. Thus the ellipse was a result of a slow oscillation

about a stable position a circle round the central body com-

pared by Borelli to the oscillation of a pendulum, to and fro,

passing through a stable position at the perpendicular. This hypo-thesis was in accord with the observed fact that the velocity of the

planet is greatest at its nearest approach to the sun.

Borelli's theory, an amalgamation of those of Kepler and

Descartes, in regarding the planets as impelled by a sort of vortex

centred upon the sun conceived of the universe as a driven, not

a free-spinning, machine. To it the law of inertia could not be

directly applied hence Borelli's confusion concerning force andmomentum. Both Hooke and Newton took two more important

steps: they assumed that the planetary motions were purely in-

ertial the universe was a great top and that there was a uni-

versal, mutual attraction between masses of matter. Newton,moreover, remedying the mistakes in the principles of dynamics

1Nearly two hundred years later, Clerk-Maxwell accounted for the stability

of the innumerable small satellites which compose Saturn's rings in a mathe-matical analysis, the principle ofwhich was dimly anticipated in this hypothesisof Borelli.


which permeate Borelli's treatise, effected a meticulous analysis

of the forces which the latter (and Hooke) had described so

loosely.

There is ample evidence that by 1685 Robert Hooke had a very

complete picture of a mechanical system of the universe founded

on universal gravitation. In the early days of the Royal Society he

performed unsuccessful experiments to discover whether gravityvaries above and below the earth's surface. In Micrographia (1665)he conjectured that the moon might have a 'gravitating prin-

ciple5

like the earth. In a discourse read to the Royal Society in

1666 Hooke improved on Borelli with the supposition that a

'direct motion* might be inflected into a curve by 'an attractive

property of the body placed at the centre.' 1 Like earlier writers he

compared this centripetal attraction to the tension in the string

of a conical pendulum, which retains the bob in its circular path.In 1678 he wrote: 'I suppose the gravitating power of the Sun in

the center of this part of the Heaven in which we are, hath an

attractive power upon all the planets, . . . and that those againhave a respect answerable.' 2 This is the first enunciation of the

true theory of universal gravitation of gravity as a universal

principle that binds all the bodies of the solar system together.The same force whereby the heavenly bodies 'attract their own

parts, and keep them from flying from them,' also attracts 'all

the other celestial bodies within the sphere of this activity.5

It is

this force which, in the sun, bends the rectilinear motions of the

planets into closed curves. And this force is'

the more powerful in

operating, by how much nearer the body wrought upon is' to the

attracting body.3

These ideas, Hooke claimed, he had expounded as early as

1670. But it was not until 1679 that he hit upon a hypothesis to

describe the rate at which the gravitational attraction should de-

crease with distance. In that year he renewed his correspondencewith Newton, discussing an experiment to detect the earth's rota-

tion through the deviation of falling bodies. This in turn led to a

debate on the nature of the curve which a heavy body woulddescribe if it were supposed to be able to fall freely towards the

centre of the earth, during which (in a letter to Newton dated

1 R. T. Gunther: Early Science in Oxford, vol. VI (Oxford, 1930), p. 266.*

Ibid., vol. VIII, p. 228.3

Ibid., vol. VIII, pp. 27-8, 229-30, etc.


6 January 1680) Hooke stated the proposition that the force of

gravity is inversely proportional to the square of the distance,

measured from the centre of the gravitating mass. 1 He was con-

vinced that this"inverse square law" of attraction, combined

with the ideas he had already sketched out, would be sufficient to

explain all the planetary motions.

Hooke's scientific intuition was certainly brilliant. Of all the

early Fellows of the Royal Society, in a generation richly endowedwith genius, his was the mind most spontaneously, and sanely,

imaginative; schemes for new experiments and observations oc-

curred to him so readily that each day was divided between a

multiplicity of investigations; physiology, microscopy, astronomy,

chemistry, mechanics, optics, were each in rapid succession sub-

jects for his insight and ingenuity. No topic could ever be broached

without Hooke rising to make a number of pertinent points andto suggest fruitful methods of inquiry. With regard to celestial

mechanics, Hooke's conception was as far-reaching as Newton's;but it was not prior and it was not proven. The publication of the

Principia, accompanied by Hooke's charge of plagiary against

Newton, inflamed the suspicion between the two men into out-

raged anger. Both suffered from a touchy pride; neither would

recognize the true merits of the other. In Newton's eyes, Hooke

grasped after other men's achievements, having merely patched

together some notions borrowed from Kepler, Borelli and Huy-gens. To Hooke, Newton had merely turned into mathematical

symbols ideas that he had himself already expressed without at-

tracting notice or reward. He was ever unwilling to admit the

supreme advantage that Newton held over himself, of beingmathematician enough to demonstrate as a theory, confirmed byobservation, that which Hooke himself had only been able to

assert as a hypothesis. In fact the different status which attaches

to a scientific theory and a scientific hypothesis a difference which

1 Hooke thought that this same law would apply to the force of gravitybelow the earth's surface. Newton later proved (Principia, Bk. I, Prop. LXXIII)that within a sphere the centripetal force is inversely proportional to the dis-

tance from the centre, not to the square of the distance. Ismael Bouillau, in

Astronomia Philolaica (1645), had argued that the intensity of Kepler's "moving

virtue" resident in the sun would decrease, like that of light, as-TJ. Therefore,

he said, since the velocities of the planets are not in this proportion to their

distances from the sun, they could not be impelled by such a force emanatingfrom it.

a68 THE SCIENTIFIC REVOLUTION

Newton emphasized more than once was something to which

Hooke proved himself insensitive by a number of episodes in his

career. As Newton pointed out, Hooke did not invent the theoryof attractive forces, as such; and after Huygens' theorems on the

centrifugal acceleration of rotating masses had been published,the inverse square law could easily be deduced. Granting the

highest merit to Hooke's scientific intuition, it is quite clear from

certain confusions inherent in the development of his hypothesisbetween 1666 and 1685 that his mastery of the principles of

dynamics was never completely confident, and that his thoughtwas never safeguarded by the precision of mathematical analysis.

Newton complained, in a letter to Halley at the time whenHooke was voicing his protests before the Royal Society, that the

latter wished to assign to him the status of a mathematical drudgeand claim for himself the sole invention of a new system of celestial

mechanics. The truth is far otherwise. By 1666 Newton was al-

ready able to calculate centrifugal accelerations. This calculation,

applied to Kepler's laws, gave him the inverse square law of

attraction. 1 If the earth's gravitational attraction was assumed to

act upon the moon, he computed that in accordance with this law,

at the distance of the moon from the earth this centripetal force

would be "pretty nearly" equal to the centrifugal force created

by the moon's own revolution about the earth. Gravity would be

precisely the chain required to bind the moon in its orbit. 2 But

such a calculation was not strictly appropriate: for a planet's

(and the moon's) orbit is not circular but elliptical, with the central

body (sun or earth) at one focus of the ellipse. Moreover, in calcu-

lating the distances and relative forces, Newton had proceeded as

though the earth and moon were points, that is, reckoned that if

flr

the force of gravity at the surface of the earth was,then at the

1 In a circle of radius r, if T is the time taken by a body to complete onef

revolution, the centripetal force required to hold it in its path is F = ~=5. But

according to Kepler's Third Law, in the solar system T2 = A'r3 . Substituting,

F =^3 whence, omitting the constants, F is proportional to

r,.

2 Newton's calculation in 1666 did not give a perfect confirmation of the

inverse square law, because the value he took for the earth's radius (and hencethe distance of the moon from the earth) was too small. It used to be supposedthat this discrepancy induced him to lay the matter aside. The view given belowis now generally accepted.


gmoon it was 7^-\ 2

- He had not proved that the external gravita-

tional attraction of a sphere could be computed as though its mass

were concentrated in a point at the centre. The difficulties in-

volved in perfecting the hypothesis upon which his first casual

trial was founded were mainly mathematical, and at this time

beyond Newton's skill. So great were they that Halley was aston-

ished to learn (in 1684) that Newton had overcome them; had

proved, in fact, that the path followed by a body, moving obliquelyin relation to a second which exerts a centripetal force upon it,

must correspond to one of the conic sections. 1

In 1666, therefore, Newton was not satisfied that the inverse

square law represented more than an approximation to the truth.

Impressed by the mathematical difficulties involved, he laid the

hypothesis aside. For about thirteen years (1666-79) there is not

the least evidence that he paid any attention to dynamics, uni-

versal gravitation or celestial mechanics. Optics, mathematics,

alchemy and perhaps already theology, filled his mind. So much,at least, Newton owed to Hooke: that he was compelled to return

to his former hypothesis. Even when driven, by Hoove's unwel-

come letters, to review the mystery of gravity, he was guilty of

blunders and misapprehensions. Even when, pricked by Hooke's

corrections, he had solved the problem of the inverse square law

and the elliptical orbit, Newton once more set his success to cool

for a further five years. Only Halley's visit to Cambridge in 1684,and the warmth of his admiration and offers of assistance, set the

Principia in train.

The book is often described as though its sole function was to

establish what has been called the Newtonian system of the uni-

verse. That it did so is, indeed, its main historical importance; the

Third Book and the System of the World, in which Newton set him-

self directly to this task, are likely to be read with far greaterinterest than the earlier sections. But Newton's influence on subse-

quent science, in this work alone, penetrated to a far greater

depth. He defined mass and the laws of motion. He gave to science

formal concepts of space and time which needed no revision for

1 Newton established (Principia, Bk. Ill, Prop. XL) that the path of a cometis a parabola, and that the orbit of a returning comet, such as that examined

by Halley (&/., Prop. XLI), is an extended ellipse of which the portion near.the sun is scarcely distinguishable from a parabola.


two centuries. He expounded and exemplified a "method of

philosophizing" that is still regarded as a valid model. He virtually

created theoretical physics as a mathematical science in the form

which it preserved to the end of the last century. For Newton, the

mathematical principles in nature were not merely evidenced bythe elementary dynamics of Galileo, or even by his own majestic

computations relating to the planetary motions, but were to be

traced in the whole field of experimental physics and more

conjecturally in the phenomena of light, in the constitution of

matter and the operations ofchemistry. Outside physics, Newton's

work was never finished it could not be finished and his ideas

remained half-formed. The Principia, however, is a treatise on

physics almost as much as it is a treatise on celestial mechanics;and in some sections Newton made meticulous use of the quantita-tive experimental method. l The theorems and experiments on the

vibrations of pendulums in resisting media, on the free fall of

bodies and the trajectory of projectiles in the same, are not perhapsof great intrinsic interest, as certainly they were of no practical

importance, nor closely relevant to the motions of the planets; but

it is not impossible to understand why Newton concerned himself

with them. For, firstly, such problems were close to the heart of

seventeenth-century physics, in a tradition which Newton himself

brought to a climax. And secondly, they served to prove his pointthat the principles of nature are mathematical; that with numberand measure science could reach beyond the uncontrolled imagina-tion of a Descartes, or even the idealism of a Galileo. In Newton's

eyes, scientific comprehension was not limited to vague qualitativetheories on the one hand, or definite statements about a state of

affairs much simpler than that which is actually experienced onthe other; it could proceed, by due techniques, to definite ideas

about all that is physical, down to the properties ofeach constituent

corpuscle. To illustrate this conception of science is the purpose of

the Principia.

Otherwise, both logically and emotionally, the framework of

celestial mechanics would have been without foundation. HereNewton and Descartes were more alike than the crude antithesis

of their cosmologies would allow. Descartes had proceeded, in the

Principles of Philosophy, from his clear ideas of what must be,

1 Thus, fresh experiments on the descent of heavy bodies in resisting mediawere added by him to each of the later editions of 1713 and 1726.


through the laws of motion and the properties of moving bodies,

to his celestial mechanism. Newton likewise: developing his

mathematical method from the definitions and the laws of

motion, through the long analyses of the motions ofbodies in manydifferent circumstances until he could discern in the heavenlymotions special cases of those principles of motion that he had

already elucidated. Newton perceived, as Descartes had done, as

Huygens did when he all but abandoned Descartes, that a theorywhich attributed the most noble and enduring phenomena in

nature to the play of mechanical forces could not stand on a

handful of assumptions, two or three happy computations and the

vague, undemonstrative, mechanistic philosophy that had becomefashionable. 1 Like Descartes, but with an infinitely more subtle

logic, with all the rigour of mathematics and with cautious appealto observation and experiment, Newton displayed the whole

science of matter-in-motion before he turned to the solar system

specifically. An unfinished treatise, De Motu Corporum, precededthe Principia\ the study of a particle in motion must precede that

of a circling planet. And if Newton found it necessary to investi-

gate the solid of least resistance, or the flow of liquids, it was to

prove the universality of that science of moving particles that he

proposed to apply, not to a minute part, but to the whole of man's

physical environment. The Principia, in fact, does not expound a

particular scientific theory to account for the motions of the

heavens: it develops a theory of physical nature which embraces

these phenomena, and all phenomena of matter-in-motion, within

its compass.As such it was, of course, a mechanistic theory. No other was,

or is, conceivable within the range of physics. Not that Newtonexcluded God from the universe:

This most beautiful system of the sun, planets, and comets, could only

proceed from the counsel and dominion of an intelligent and power-ful Being. . . . He endures forever, and is everywhere present; and

by existing always and everywhere, he constitutes duration and

space.2

1 In this, of course, Newton powerfully revealed his immense superiorityover Hooke, who could never have constructed the laborious scaffolding uponwhich Book III of the Principia is raised.

1 General Scholium, concluding the Principia. Cf. Florian Cajori: Sir Isaac

Newton's Mathematical Principles ofNatural Philosophy (Berkeley, 1946), pp. 544-6.


God was for Newton the Final Cause of things, but, excellent and

laborious theologian as he was, he made no confusion between

physics and theology.1 That Newton seemed, by the theory of

universal gravitation, to contravene the principles of mechanism,was due to misapprehension. Though certain phrases in the Prin-

cipia might seem to indicate the contrary, he did not believe

that gravity was an innate property of matter, nor that two

masses could attract each other at a distance without having anymechanical relationship. To Bentley Newton wrote:

It is inconceivable that inanimate brute matter should, without the

mediation ofsomething else, which is not material, operate upon andaffect other matter without mutual contact. . . . That gravityshould be innate, inherent, and essential to matter, so that one bodymay act upon another at a distance through a vacuum, without the

mediation of anything else, by and through which their action andforce may be conveyed from one to another, is to me so great an

absurdity that I believe no man who has in philosophical matters a

competent faculty of thinking, can ever fall into it.2

He added to the second edition of the Principia a brief statement

that by attraction he meant only to describe the tendency of bodies

to approach each other, no matter what the cause. As to the prob-able nature of this cause, he professed himself ignorant.

3 It was

sufficient to infer that the phenomenon existed and was universal;

like Galileo, Newton regarded the effect as established if it could

be described, though the cause were hidden. To suppose that par-ticles or masses exert a gravitational attraction was not, therefore,

in Newton's language to postulate an occult quality in matter but

to describe a fact a fact that was to be demonstrated in the

laboratory by Henry Cavendish seventy years after Newton's

death. Nor did Newton believe that the celestial spaces across

which the sun's attraction holds the planets in their orbits were

necessarily empty of all matter.

His refusal to ascribe a cause or mechanism to universal gravi-tation was indeed one of Newton's principal advantages in celes-

1 Newton, however, expressed a sentiment typical of the age in a letter to

Bentley (1692): 'When I wrote my treatise about our system, I had an eye onsuch principles as might work with considering men for the belief of a Deity;and nothing can rejoice me more than to find it useful for that purpose.' (Ibid.,

p. 669).1Quoted by Cajori, op. '/., p. 634.

* In a letter to Boyle, he outlined a theory of actherial contraction which henever troubled to develop thoroughly.


tial mechanics. He was free, as the Cartesians were not, simply to

state and analyse the observable facts, and the inferences neces-

sarily drawn from them. He did not seek to construct a modelwhich would be rendered clumsy and contradictory by the

very attempt to explain everything in nature by corpuscularmechanisms.

Hypotheses [wrote Newton], whether metaphysical or physical,

whether of occult qualities or mechanical, have no place in experi-mental philosophy. . . -

1 And to us it is enough that gravity does

really exist, and act according to laws which we have explained, and

abundantly serves to account for all the motions of the celestial

bodies, and of our sea. 1

The concluding paragraph of this General Scholium indicated a

possible solution of many "occult" mysteries, fully in the

seventeenth-century mechanical tradition. For,

We might add something concerning a most subtle spirit which per-vades and lies hid in all gross bodies; by the force and action ofwhich

spirit the particles of bodies attract one another at near distances, and

cohere, if contiguous; and electric bodies operate tp greater dis-

tances . . .; and light is emitted, reflected, inflected, and heats

bodies; and all sensation is excited, and the members ofanimal bodies

move at the command of the will. . . .

Newton's imagination was not less generous than that of Descartes,

though less dogmatic. He was as fully convinced of the existence

ofan ather, the residuum ofthe major secrets ofnature, as Descartes

or any nineteenth-century physicist. Further hints were to be given

years later in the Queries appended to the Opticks, but Newton did

not know how these things could be investigated, much less proved.

Nevertheless, his attitude (less plain certainly in the first edition

of the Principia than it has since become) was widely misunder-

stood. Newtonian empiricism was rapidly accepted by his own

countrymen: probably no scientist has received a more immediate,or a warmer, acclaim from the intellectuals as well as the professedscientists of his race. Abroad it was distrusted. Neither Huygensnor Leibniz (who set the tone for many lesser men) could stomach

1Newton, of course, did not mean that tentative hypotheses have no use in

an investigation; he framed many such himself. He meant that an unconfirmedand undemonstrated hypothesis should not be taught as an adequate theory.

1Gajori, op. cit. y p. 547.


the downright statement of Proposition VII, Book III. 1Attempts

to reconcile the Cartesian mechanical theory of celestial vortices

with Newtonian mathematical laws were prolonged into the mid-

eighteenth century. Not until fifty years after the publication of

the Principia did Voltaire's proclamation of his admiration for the

profound English geniuses, Newton and Locke, begin to win ad-

herents. The essential truth, that Newton and Descartes shared

the same idea of nature, was thus long obscured; and Newton has

perhaps been too often praised for being other than he was. Theidol of perfection who was endowed by the nineteenth centurywith every attribute of scientific insight and vigour, with abhor-

rence of hypothesis and mystery, with serene temper and con-

ventional religion, was not the genuine Newton. It is perhaps

paradoxical but not unjust that his greatest successor was to

arise not from the crowd of reverend English gentlemen who were

to claim Newton as their own, but in the person of the sceptical

French mathematician, the Marquis de Laplace, whose MlcaniqueCtleste (1799-1825) extended in time the laws that Newton hadtraced in space.

1 ' That there is a power of gravity pertaining to all bodies, proportional to

the several quantities of matter which they contain.'

CHAPTER X

DESCRIPTIVE BIOLOGY AND SYSTEMATICS

BIOLOGICAL

study, as it is practised today in laboratories andfield stations, is essentially a creation of the nineteenth

century. The work of Darwin on evolution, of Mendel on

genetics, of Schleiden and others on the cell theory, so transformed

the texture of the biologist's thought that it would be appropriateto attribute to the period 1830-70, rather than to any earlier age,the "biological revolution" which completed the modern scien-

tific outlook. The belief in the fixity of species was no less respect-able than the belief in the fixity of the earth; the belief that the

Creator must have personally attended to the fabrication of everykind of diatom and bramble was no less primitively animistic thanthe belief that His angels governed the revolutions of the planetaryorbs. Exactly as the mechanistic philosophy of the seventeenth

century was accused of encouraging scepticism and irreligion, ona greater scale (because the issue was more clear and more

decisive) the mechanistic biologists of the nineteenth met the full

force of ecclesiastical wrath. The liberty of the scientist to direct

his theories in accordance with the scientific evidence alone was

equally at stake. But there is this difference. Biology was certainly"modern" in some respects if not all before the nineteenth

century. A great renaissance had already occurred, which itself

far surpassed all that had gone before. Materials had been heapedup from which a great generalization such as evolution could be

drawn. Above all, the scientific method of biology was already in

existence that was not the creation of the nineteenth century.The researches of Leeuwenhoek and Malpighi, the systematics of

Ray and Linnaeus, were preliminaries as essential to the syntheseswhich introduced the truly modern outlook as the work of

Copernicus and Galileo was to that of Newton.None of the ancient founders of biology was primarily in-

terested in collection, description and classification as ends in

themselves. Aristotle the zoologist and Theophrastus the botanist

were always philosophers their purpose was to investigate the

275


functioning of living organisms; Dioscorides studied botany as the

servant of medicine. Partly, perhaps, because the range of species

examined was comparatively small neither Aristotle nor Theo-

phrastus knew more than about five hundred distinct kinds of

animals or plants the problem of cataloguing them did not

become ofoverriding importance, though much thought was givento order and arrangement. Since the Greek empire extended into

India, exotic species were available, but they did not attract

great attention. 1 To the Greek mind, the attempt to answer the

questions that living nature posed was more important than the

compilation of information, and for this the materials close at

hand were sufficient. Over-leaping a great space of time, in the

last century collection and taxonomy have again become no morethan specialized branches of biology. The study of function, of

the processes of growth and differentiation, has assumed a morefundamental importance. The experimental has replaced the

encyclopaedic method, so that a modern zoologist may find a

greater interest in the works of Aristotle than in those of anynatural historian of the pre-Darwinian age.

The intervening period has, indeed, very special characteristics.

For long there were no adequate successors to the Greek botanists

of the fourth century B.C. The Romans were competent writers on

agriculture, but such an author as Pliny added nothing beyondthe cult of marvels to the existing texts which he pillaged. The

philosophic spirit of the Greeks almost perished, and was onlyrevived in the botanical work of Albert the Great (De Vegetabilibus

et Plantis, c. 1250). Albert was an Aristotelean botanist at least,

his main authority was a translation of two books on plants then

attributed to Aristotle. 2 He was interested in the philosophy of

plant growth, in the variety of their structures and (as he believed)in their constant mutations. Care in the morphological analysisof plants for purposes of description and identification was com-bined with renewed attention to the problem of classification, but

Albert was not greatly impressed by the importance of cata-

loguing. Such an emphasis was then unusual, for in his time

herbalism medical botany had already become a principalinterest. It is a strange paradox that while the learning of the

1 One important exception was the date-palm, which provided the onlyexample of sexuality in plants known before the late seventeenth centu

* But now assigned to Nicholas of Damascus (first century B.C.).

DESCRIPTIVE BIOLOGY AND SYSTEMATICS 277

later middle ages turned so naturally to argument in metaphysicsand philosophy, and thence to logic, cosmology and physics, the

intellectual problems posed by the living state were so often

ignored. Only in its relations with medicine can medieval biologybe generally said to have had a serious intellectual content, to

have attempted to answer questions.Herbalism looked to Dioscorides, rather than to Aristotle and

Theophrastus. Before the fall of Rome the tradition he founded

had already suffered debasement and the decline, both in matter

and in illustration, continued throughout the early middle ages.In the thirteenth century, however, there were already skilful

herbalists with a good knowledge of Dioscorides and his com-

mentators, some familiarity with exotic drugs, and an interest in

description and identification. The herbal ofone of them, Rufinus,serves to show that he, at least, did not scruple to add remarks

of his own to the literary tradition, and that he was aware of

distinctions in kind unknown to the more famous compilers of

the sixteenth century.1 Rufinus was clearly well acquainted with

drug plants and druggists, but he made no attempt to classify,

merely arranging his notes in alphabetical order. The greater partof his text was made up ofquotations from earlier pharmacologicalauthorities (Dioscorides, the Circa instans of about 1 150, the Tables

of Salerno, and others) ,but Rufinus' own additions were mostly

botanical, such as this description of Aaron's Beard:

Aaron's Beard has leaves which are thick in substance, nearly a spanbroad and long, and it has two little beards to each leaf. The leaves

are divided down to the root. It has a tuberous root in the ground,from which a cosmetic ointment is made, and it sometimes has

blotched leaves. It forms its flower in a capsule, contrived by a

marvellous artifice and having this yellowish capsule around it, in

the centre of which is a sort of finger, with two little "apples" below

it, wonderfully contrived. The plant which has blotched leaves is

masculine and that without blotches on the leaves is feminine. 2

His manuscript was apparently unillustrated, so that the identifi-

cation ofuncommon plants from it would have been very doubtful.

The herbal flourished, to become enormously popular soon

after the invention of printing. But the herbalist's interest in the

plant was always in knowledge of means to an end. Some of his

1 Lynn Thorndikc: The Herbal of Rufinus (Chicago, 1946).*

Ibid., p. 54.


medicaments were minerals, or derived from animal sources, and

it was only because such a large proportion of medieval physicwas derived from vegetables, that the pharmacopoeia assumed a

preponderantly botanical form. Thus descriptive zoology was a

poor relation of herbalism, though animals were also described

as the immediate companions and servants of man, because theyoffered useful moral lessons, and because some of them had an

exotic or symbolic fascination. Conceiving that the world was

created for the use and instruction of man in working out his

own salvation, the medieval mind naturally adopted a somewhatfunctional approach to the living state. The task of the naturalist

was simply to describe living things, with their particular uses (or

wonders, or edifying properties) so that other men might use them

(or wonder at them, or be edified). Despite the occasional philo-

sophic questioning of an Albert, there was no powerful motive to

elevate him above a lexicographical mentality. And the naturalist

was less interested in collecting facts about creatures that mightform the material of a science, than in human reactions to this

and that, in the diseases against which a given plant was supposedto be beneficial, in the moral to be drawn from the habits of the

ant-lion.

Thus the origins of natural history were essentially anthropo-

centric, in the Roman Pliny, in the early Christian compilers like

Isidore of Seville, in the thirteenth-century encyclopaedia of

Bartholomew the Englishman, in the late medieval herbalists.

Human interest in nature was limited to the production of a

catalogue raisonnt.

The early stages of the renaissance brought no important re-

orientation. Occasionally the representational art of a "Gothic"

stone mason or wood carver had enriched a cathedral with a

recognizable likeness of a living species. About the beginning of

the fifteenth century the graphic artist began to realize the

aesthetic possibilities ofexact imitation ofnature in the illumination

of manuscripts here were the roots of both the naturalistic art

of a Durer, and biological illustration. By 1550 the technique of

life-like illustration had been mastered, with greatest distinction

in the herbals ofBrunfels (1530) and Fuchs (1542). This techniquewas ultimately as necessary to botany and zoology as to humananatomy, but it did not occasion any immediate enhancement of

the level of botanical knowledge, for the texts of both Brunfels'


and Fuchs' books were poor, and excelled in description byunillustrated works, such as that of Valerius Cordus. Brunfels,

indeed, tried to find some more natural arrangement than that

of an alphabetical list, but the latter was by no means abandoned

as yet. The botanists of the sixteenth century, with the exceptionof Cesalpino and Gesner, were still herbalists, and the herbal wasstill an adjunct to the pharmacopoeia, enabling the apothecary to

identify such medicinal plants as Swallow-wort and Fennel, Sageand Fumitory, whose names are perpetuated on the delightful

majolica drug-pots of the time.

Humanism had its effect upon biology, as upon all branches of

science, without challenging the main emphasis on collection andclassification. The authority of Dioscorides and Theophrastus wasreinforced rather than weakened; their texts were better under-

stood, but did not encourage originality in ideas. Mediterranean

botanists particularly took up the task of identifying more exactlythe species described by Dioscorides; some, like Mattiolo, Cordusand Conrad Gesner, were content to put forward their own workas expansions of his, with considerable display of philological

learning. Gradually it was learnt that Greek names had been

abused by application to species quite different from those knownto the Greeks themselves; and that, moreover, the name often

covered a whole group of similar plants, not a specific type.Northern botanists, on the other hand, acquired knowledge of

plants not included in the traditional Mediterranean flora; Charles

de rficluse alone is reputed to have found two hundred new

species in Spain and Portugal (1576), and later he was equallysuccessful in Austria and Hungary. Cataloguing and descriptionwere extended far beyond the range of the merely useful. Decora-

tive plants, like the daffodil and horse-chestnut this last one of

many importations into western Europe at this period werenoticed as well as the medicinal, along with many new species

reported by the explorers to the Far East and the Americas. Thecommon and uncommon plants of hedgerow, pasture and uplandwere no longer neglected. A garden was now judged by the

multitude, rarity and beauty of the species represented in it, while

the Hortus Siccus became a repository of trophies exchanged amongcollectors. For the men of the renaissance collected plants,

plumages and skins as they amassed coins, antique statuary and

manuscripts, since greater wealth and leisure permitted such


costly and learned ostentations. The plants in some renaissance

gardens, like that of the Venetian patrician Michieli (c. 1565),were commemorated in water-colour and written description.

Though the character of the product of this vastly increased

activity in botany, or herbalism, was not greatly changed in the

sixteenth century, the character of the new herbalist was certainly

modified. As he attached less importance to medicinal value, he

became more keenly interested in fine distinctions; whereas the

ancient and medieval herbalist had hardly been concerned with a

unit smaller than the genus, their successors began to discriminate

between different species within the genera, and even between

varieties of the same species. Again, the new naturalists were often

scholars and gentlemen, they had therefore greater opportunitiesfor botanizing over wide areas, even despatching emissaries for

this purpose; they could acquire a more extensive literary know-

ledge and employ the best draughtsmen. Doubtless such men felt

the aesthetic appeal of nature more keenly than the apothecary or

peasant. As Fuchs wrote:

There is no reason why I should expatiate on the pleasure and delightof acquiring knowledge of plants, since there is no one who does not

know that there is nothing in this life more pleasant and delightfulthan to wander over mountains, woods and fields garlanded andadorned with most exquisite little flowers and plants of various sorts.

. . . But it increases that pleasure and delight not a little, if there be

added an acquaintance with the virtues and powers of these plants.1

Fuchs' observation ends with a touch ofthat pedantry which has

always divided the scientist from the artist; the scientific tendency

is, after all, to dissect and destroy the thing of beauty, but there is

no reason to doubt that the intellectual inquisitiveness which leads

via microscope and herbarium to the unreadability of a Flora, mayhave its aesthetic foundation. This also links naturally with the

urge to collect and preserve, the emphasis upon the rare and the

expensive, which are so typical of biology from the sixteenth to

the nineteenth century. Collector's mania has often been derided,

yet it may yield genuine scholarship, as in (for example) the studyof ceramics or bibliography. The botanist's character was more

complex. He could claim that his activities were useful to man,and contributed to the worship of God. If Sir Joseph Banks'

1 De Historia Stirpium (Basel, 1542), Preface, sig. otav. Quoted by A. Arber:Herbds (Cambridge, 1953), p. 67.


attempts to transplant the breadfruit to the West Indies were

vain, naturalists had great success with tobacco, the potato, maizeand innumerable ornamental species. In nature they saw abund-ant evidence of Design, and so created the tradition which led

through Ray's Wisdom of God to Paley's Natural Theology, or

Evidence of the Existence and Attributes of the Deity, collectedfrom the

Appearances of Nature. There was thus a variety of arguments for

commending biology to the attention of a serious and devout

mind, of which medical utility was not the least important. Fewnaturalists in this period would have given whole-hearted supportto the views of the Bohemian, Adam Zaluzian (1592):

It is customary to connect Medicine with Botany, yet scientific treat-

ment demands that we should consider each separately. For the fact

is that in every art, theory must be disconnected and separated from

practice, and the two must be dealt with singly and individually in

their proper order before they arc united. And for that reason, in

order that Botany, which is (as it were) a special branch of Natural

Philosophy, may form a unit by itself before it can be brought into

connection with other sciences, it must be divided and unyokedfrom Medicine. 1

The task of the descriptive biologist was also far more complexthan that of the cataloguer of human artifacts, indeed, it was this

complexity which enforced the development of systematics. Prob-

lems of nomenclature, identification and classification rather

suddenly became acute between 1550 and 1650, and constituted

one of the main theoretical topics in biology for nearly three

hundred years. Naturalists tried to follow a "natural" order of

groupings which meant that they were long deceived by superficial

characteristics. Aristotle had distinguished, in zoology, between

viviparous and oviparous creatures, between the cephalopodia and

other molluscs; Dioscorides had distributed plants among the four

rough groups of trees, shrubs, bushes and herbs. Lesser distinc-

tions, between eggs-with-shells and eggs-without-shells, between

deciduous and non-deciduous, flowering and non-flowering, were

also very ancient. In the main such distinctions were preserved as

the basis of arrangement until late in the seventeenth century.Nomenclature was equally in need of reform, if standardization

was to be obtained, and the name to have a logical connection

with the system. Description was the very basis of a communion1 Methodi Herbaria Libri Tres, quoted in Arber, op. '/., p. 144.


of understanding in biology, for on it depended the hope of arriv-

ing at a single comprehensive Flora which would enable all mento agree upon the identity ofany given specimen. Here the classical

tradition was very frail, partly owing to the defects of its languagein referring to the parts of animals and flowers.

No consistent answers to the problems of taxonomy were pro-duced before the eighteenth century; even today the concept

"species" cannot be exactly defined, and many systems of classifi-

cation have succeeded that of Linnaeus. Nevertheless, the great

compilers of the sixteenth century, in their attempts to make an

encyclopaedic survey of all living things, more than mastered

their Greek inheritance and demonstrated the fruits of exact ob-

servation. Their view of their undertaking was of course far from

strictly biological. Thus Conrad Gesner, in his enormous Historic

Animalium (published 1551-1621), besides naming and describingthe animal, discussed its natural functions, the quality of its soul,

its use to man in general and as food or medicine in particular, and

gave a'concordance ofliterary references to it. The Italian natural-

ist Ulissi Aldrovandi strove for even deeper omniscience when (for

example) writing of the Lion he noted at length its significance in

dreams, its appearance in symbolism and mythology, and its use

in hunting and tortures. But Aldrovandi was also one of the first

zoologists to give a skeletal representation of his subjects where

possible. Along with the spirit ofsheer compilation there developeda growing tendency to specialize, exemplified in Rondelet's bookon Fishes (1554), in Aldrovandi's treatise on the different breeds

of dog, in the Englishman Thomas Moufet's Theatre of Insects

(1 634) .

x All these works, and some portions of the vast encyclo-

paedias, were written with conspicuous attention to the kind of

detail that could only be obtained through systematic personalobservation. Most of the old fables debasing natural history the

birth of bees from the flesh of a dead calf, and of geese from

barnacles, the inability of the elephant to bend its legs, and the

tearfulness of crocodiles were at least doubted, though they

lingered long in popular books.

The classification of animals in accordance with Aristotle's

scheme presented no great difficulties. The Latin names gavesufficient identification, superficial distinctions were marked. In the

1This, written about forty years earlier, was largely compiled from the

work of Thomas Penny (c. 1530-88).

DESCRIPTIVE BIOLOGY AND SYSTEMATIGS 283

group of oviparous quadrupeds, for instance, Gesner had only a

few divisions frogs, lizards, tortoises and he knew only three or

four different kinds in each. Plants were more recalcitrant. Alpha-betical lists had their uses, and so had others in which the groupsconsisted of plants having a similar habitat or function. When the

attempt was made to render identification easier by adopting

arrangements based on form and structure, more profound diffi-

culties were encountered. In general, it seemed desirable to makethe arrangement as natural as possible, by taking into considera-

tion the maximum number of characteristics, but it was difficult

to decide what the most important of these were. Reliance on

superficial features, like the possession of prickles, or habits like

climbing, was apt to prove very deceptive. The early systematists

consequently tended to make increasing use of a single character-

istic of the plant as a determinant de PObel chose the leaf, and

Cesalpino the fruit. One advantage of this method was that it led

to the more intensive study of particular parts of the plant, espe-

cially the flower, and to the improvement of descriptive termi-

nology. Such systems, of which Linnaeus' was the logical and

highly successful climax, were artificial, convenient indices to the

prodigality of nature; but they did promote conscious study of

the problems of taxonomy. Before 1550 there were hardly anyfirm principles by which species were distinguished, while the

arrangement of the species was a matter for the discretion of

each author. By 1 650 there was a great measure of agreement on

specific identities, and it was gradually becoming clear that

there was a difference between a search for a method, which wouldmake identification easy, and an endeavour to trace the natural

affinities between species and larger groupings.Attention to systematics was partly enforced by the sheer multi-

plicity of species. Some six thousand distinct plants had alreadybeen described by 1600, and the number trebled during the follow-

ing century. Since it was the pride of the good botanist to be able to

identify every plant presented to him, or if it were a new species to

indicate its relationship to known ones, there were strong reasons

for correlating identification and arrangement with one or more

morphological. characteristics. Caspar Bauhin, in 1623, outlined

the natural groupings of botanical species more clearly than anyof his predecessors, and made more extensive use of the binomial

nomenclature in which one element of the name was shared by the


genus, or group of closely related species. A little later Jung, at

Hamburg, greatly improved the technical description of the dis-

position and shape of leaves, and of the various parts of the flower.

A younger contemporary, the EnglishmanJohn Ray (1627-1705),laid the foundations of modern descriptive and systematic biology,in botany at least owing something to Jung's methods. Ray hadsome experience of dissection, but he was not an experimenter, nor

a microscopist. Though his interests extended to the ecology, life-

history and physiology of his subjects thus he was much morethan a plain cataloguer he did not himself do much to advance

the newer branches of biology growing up in his time. On the

other hand, his philosophic and general scientific outlook was

wider than that of most succeeding naturalists; like many other

Fellows of the Royal Society, he was fascinated by technological

progress, accepted the broad picture of a mechanistic universe

under divine surveillance, andjoined in the expulsion from biologyof myth and mystery.

Ray was perhaps the first biologist to write separate treatises onthe principles of taxonomy.

1 These were exemplified in his greatseries of descriptive volumes, the Historia generalis plantarum (1686-

1704) and Historia insectorum (1710), with the Ornithologia (1676)and Historia Pisciwn (1686) in which he collaborated with his

patron, Francis Willughby. Taken together for all these books

were actually written and published by Ray they represented

by far the most complete and best arranged survey ofliving nature

that had ever been attempted. Ray had exercised his keen facultyfor observation intensively over the whole of England, and ex-

tensively over much of western Europe; he was deeply learned in

the writings of ancient and modern naturalists; above all, he wel-

comed new ideas. From Grew he accepted as probable the sexual

reproduction of plants; from Redi and Malpighi the experimental

disproof of spontaneous generation; and he himself taught that

fossils were the true remains of extinct species, not mere "sports"of nature nor God-implanted tests ofman's faith in the truth of the

Genesis story. If the enumeration of species was his principal task

which still left him room for his Collection of English Proverbs,

Topographical Observations, and Wisdom of God Ray was very far

from supposing that classification was the end of biology.In botanical systematics Ray favoured a "method" which was1 Methodus plantarum nova ( 1 682) ; Synopsis methodica animalium quadrupedum et

serpentini generis (1693); Methodus insectorum (1704).

DESCRIPTIVE BIOLOGY AND SYSTEMAT1CS 285

more natural than those of his contemporary Tournefort and his

successor Linnaeus. He admitted that the familiar triple distinc-

tion between trees, shrubs and herbs was popular rather than

scientific, though he continued to use it while also making the far

more fundamental distinction between mono- and dicotyledonous

plants. For finer discrimination he relied upon no single character-

istic but appealed to the forms of root, leaf, flower and fruit. The

necessity for a formal method of classification was fully apparentto him it was particularly required by beginners in botany

3 B

2

11IE

Large

(Polypi, Crustacea)

Small

(Insects)

'With Lungs

Without Lungs(Fishes)

One ventricle

Heart

(Oviparous quadrupeds,Serpents)

Oviparous

(Birds)Two ventricle

< Heart

Viviparous\[Mammals]

/Cetaceans

With hoofs etc.

(Ungulates)

With nails etc.

^(Unguiculates)

Fig. 10. Ray's Classification of Animals

but he did not expect that all living forms could be perfectly ac-

commodated within it. Taxonomists would always have difficulty

with 'species of doubtful classification linking one type with an-

other and having something in common with both.' 1 In zoologicalclassification Ray was perhaps even more successful, through

basing his groups upon decisive anatomical features. He was the

first taxonomist to make full use of the findings of comparative

anatomy, particularly among mammals2 and with regard to such

characteristic features as feet and teeth, thereby discerning such

groups as the Ungulates, Rodents, Ruminants, etc. (Fig. 10). This

part of his work was freely adopted by Linnaeus.

1 Cf. the Preface to Methodus Plantarum, and C. E. Raven: John Ray, Naturalist

(Cambridge, 1950), Ch. viii.8 This class was recognized by Ray, though not given this name.

a86 THE SCIENTIFIC REVOLUTION

Meanwhile, the naturalist's range of observation was being

vastly extended by the microscope (Chapter 8). In the use of this

instrument the primary emphasis was still on description; at this

stage, attempts to construct elaborate theories upon the new evi-

dence were infrequent and misleading. There was opportunity for

the ramification of activity, and it was not neglected. The studyofplant anatomy, originally enforced by the need for classificatory

systems, could now proceed to the structure of tissues and repro-ductive mechanisms; zoological anatomy, likewise, stimulated bythe fertility of the comparative method as shown by Harvey and

many before him, was extended to strange creatures like the "orang-

outang" (dissected by Dr Edward Tyson),1and, with the aid ofthe

microscope, to levels of detail inaccessible to the naked eye.

Most of this new work prolonged existing tendencies. Marcello

Malpighi (1628-94), for example, completed Harvey's discoveryof the circulation of the blood by following its passage from the

arterial to the venous system through the capillary vessels, at the

same time observing its red corpuscles. He was also able to gofarther than Harvey and Fabricius in examining the microscopicfoetus of the chick within the first hours of incubation, from whichhe was led to believe that growth was a process of enlargement or

unfolding only: the foetus was "pre-formed" in the unfertilized

egg.2 As a pioneer of histology Malpighi entered on less familiar

ground, in his microscopic examinations of the liver, the kidney,the cortex of the brain, and the tongue, whose "taste buds" he

discovered. In the study of insects where Aristotle had shownwonderful insight the serious scientific curiosity in which Mal-

pighi was joined by Jan Swammerdam (1637-80) had alreadybeen anticipated by Hooke in Micrographia, and by even earlier

virtuosi with their "flea-glasses." These two naturalists, however,were the first to explore fully the internal anatomy of minute

creatures, demonstrating that their organs are as highly differenti-

ated as those of large animals. Malpighi's treatise on the silkworm

has been described as the earliest monograph on an invertebrate;

in it he indicated the function of the trachea first observed by him,which distribute air about the insect's body, and of other tubes by

1 Cf. M. F. A. Montagu, Edward Tyson, M.D., F.R.S. 1650-1708 (MemoirXX, Amer. Phil. Soc., Philadelphia, 1943). The creature was in fact a

chimpanzee. Tyson also published monographs on the "porpess", rattlesnake,

opossum etc.1Joseph Needham: History of Embryology (Cambridge, 1934), pp. 144 ttstq.

DESCRIPTIVE BIOLOGY AND SYSTEMATIGS 287

which the products of metabolism are excreted. He did muchwork on the anatomy of the larval stages of insects, and observed

their evolution to maturity, but here he was excelled by Swammer-

dam, who also denied that there was any true transformation, even

in the emergence of the butterfly from the caterpillar, or of the

frog from the tadpole processes which he studied with enormouscare. In sheer technical skill exemplified in the quality of his

drawings as well as in the fineness of his dissection under the lens

and his unique methods of injection Swammerdam foreshadowed

the greater manipulative resources of the mid-nineteenth century.Leeuwenhoek is chiefly remarkable for his work at much higher

magnifications and the discovery of a new world inhabited byInfusoria and Bacteria (p. 241), but the ubiquitous curiosity whichled him to examine hairs, nerves, the bile, parts of plants, crystals

indeed almost everything that could be brought before his

lenses induced him to make some observations comparable to

those of Malpighi and Swammerdam, among which those on the

compound insect eye and on ants were particularly novel. Fromobservations on aphids he discovered parthenogenesis in animals

reproduction by the female parent alone.

In the plant kingdom, the microscope could not reveal a neworder of magnitude within the living state, as it did in the animal;on the other hand, a much clearer idea of the structure of planttissues emerged including the description of their minute com-

ponents, the cells than was yet obtained in zoology. The pre-sumed anatomical and physiological analogies between animals

and plants were indeed powerful incentives to inquiry at this

time. Sometimes analogy was wholly misleading, as with the

theory (popular until disproved by repeated experiments) that

the sap in plants circulates like the blood in animals, but in other

aspects, as when the "breathing" of plants was compared with

that of animals by Malpighi and later by Stephen Hales (1679-

1761), it led towards a more correct understanding. Malpighi,

despite the excellence of his descriptions of the differing structures

found in wood, pith, leaf and flower under the microscope, andof the germination of seedlings, thought too exclusively in terms

of the animal form. Thus he wrongly identified the function of the

spiral vessels that he observed in plant tissue with that of the

tracheae in insects, and erected upon this identification a broad

theory of the increasing specialization of the respiratory organs,


reaching its climax in mammals. He also tried to find in plants

the reproductive organs familiar from vertebrate anatomy. The

Englishman, Nehemiah Grew (1641-1712), whose independentwork is closely parallel to that of Malpighi, and of equal quality,

was a more restrained observer, though he believed (as he quaintly

wrote) 'that a Plant is, as it were, an Animal in Quires, as an Animal

is a Plant, or rather several Plants, bound up into one volume' a

remark which, however strange the metaphor, expresses profoundintuition.

Grew was well aware, not only that the aims ofordinary natural-

ists still fell far short of attainment, but that these aims by no

means amounted to a true "Knowledge of Nature." His Philosophical

History of Plants (1672)* sketched a new and far more ambitious

programme. Many of the problems he proposed remain unsolved:

First, by what means it is that a Plant, or any Part of it, comes to

Grow, a Seed to put forth a Root and Trunk. . . . How the Aliment

by which a Plant is fed, is duly prepared in its several Parts. . . . Hownot only their Sizes, but also their Shapes are so exceeding various. . . .

Then to inquire, What should be the reason of their various Motions;

that the Root should descend; that its descent should sometimes be

perpendicular, sometimes more level: That the Trunk doth ascend, andthat the ascent thereof, as to the space of Time wherein it is made, is

of different measures. . . . Further, what may be the Causes as of

the Seasons of their Growth; so of the Periods of their Lives; some being

Annual, others Biennial, others Perennial . . . and lastly in whatmanner the Seed is prepared, formed and fitted for Propagation.

Some of these questions Grew himself tried to elucidate, most

brilliantly deducing that plants reproduce sexually, the flowers

being hermaphrodite like snails, with the stamens acting as the

male organs.2 Nor did he neglect the possibility of examining the

plant substance by combustion, calcination, distillation and other

experimental methods of chemistry, though these were as yet too

primitive to be of real service. In this way he showed that the

matter of the pithy or starchy part of the plant was quite distinct

from that of the woody or fibrous part. Like Ray and other

naturalists Grew saw no reason to reject mechanism as a working

1Reprinted in The Anatomy of Plants (London, 1682).

1Op. cit., pp. 171-3. Hermaphroditism is not, of course, universal among

plants, as Grew thought.


hypothesis which he developed (for example) in his account of

plant nutrition; as he put it, with a familiar simile:

[We need not think] that there is any Contradiction, when Philosophy

teaches that to be done by Nature; which Religion, and the Sacred

Scriptures > teach us to be done by God: no more, than to say, Thatthe Ballance of a Watch is moved by the next Wheel, is lo deny that

Wheel, and the rest, to be moved by the Spring ;and that both the

Spring, and all the other Parts, are caused to move together by the

Maker of them. So God may be truly the Cause of This Effect, althougha Thousand other Causes should be supposed to intervene: For all

Nature is as one Great Engine, made by, and held in His Hand. 1

A general sketch of the horizon in biology about the year 1680

would show virile activity, a steady expansion of the sphere of

interest, and the fruitful exploitation of new techniques. Ad-

mittedly Man was still the prime focus of attention, whether in

the Royal Society's endeavour to introduce a scientific spirit into

agriculture, or in the relics of the belief (still held by a plant-anatomist like Grew) that all vegetables have "virtues/

5

or in

the frequent backward glances of the zoologist at the human

body. Nevertheless, as the peripheries rapidly became more remote

they assumed, as it were, a territorial autonomy. The survival of

anthropocentricity in the feverish concentration of Swammerdamwas small. It is significant that naturalists no longer defended

their preoccupations as useful, but rather as contributions to

knowledge of the universe, of the organic part of the divinelycreated machine. And, though description and cataloguing of

macroscopic flora and fauna remained their principal tasks,

natural history showed clear signs of entering into partnershipsin which the skills of the human anatomist and physiologist,

the chemist, and the physicist, should be placed at its service.

Gradually, through the seventeenth century, biology had returned

to the philosophic attitude of an Aristotle; now it seemed likely

that the borrowing of modern knowledge and techniques would

permit the ancients to be as greatly excelled in these sciences as

in physics and mechanics.

Briefly, there was promise a promise of growth in depth andextent that was hardly fulfilled during the next century and a

half. That it was not fulfilled may be attributed partly to the

1Op. cit., p. 80.


fallaciousness ofthe early hopes, for neither microscopic technique,nor chemical experiment, were capable of changing the patternof activity so permanently as the work done during the two

decades 1660-80 would suggest. These crude tools were soon

blunted. The close connection between biology and medicine,

which had encouraged study of the former science in the seven-

teenth century, tended to hamper its later development, for as

medical studies were permeated by the influence of Galen's ideas

until the nineteenth century, it was impossible that animal and

plant studies should escape the limitations of those ideas. Unable,as yet, to build freely upwards upon the half-finished foundations

of their predecessors, eighteenth-century naturalists might well

be discouraged by the splendour of their inheritance. Discourage-ment was all the more harsh because this inheritance included

such a feeble element of hypothesis to serve as a scaffolding for

their own researches. Thereafter it is not surprising that they felt

strongly a positive attraction that was both old and new. Like the

sixteenth-century encyclopaedists, they were subjected to a vast

incursus of new species, fruit of a renewed urge towards explora-tion that drove Linnaeus into the sub-arctic tundra, and JosephBanks to the Pacific and Australasia. Moreover, this invasion

synchronized, not with a sense of confusion before the profligacyof nature, but with an increasingly dogmatic confidence in a

System, the system of Linnaeus. Quite suddenly, about the middle

of the century, classification became one of the easiest, instead of

one of the most difficult, biological exercises. Not for the first or

the last time in science there was a rush to gather the harvest,

while the unbroken fields were neglected.

Admittedly, there was no very abrupt transition. In the early

part of the century Leeuwenhoek was still active, and a little later

Reaumur, one of the most versatile experimentalists of any age,

began to publish his monumental Mtmoires pour servir d Vhistoire des

Insectes (1737-48) which continued the work of Malpighi andSwammerdam. Low-power microscopy was applied to aquatic

subjects by Trembley, who experimented upon the capabilityfor regeneration and asexual reproduction by budding that hediscovered in fresh-water "polyps" (Hydra and Plumatella),

1 and

by Ellis (Natural History of the Corallines, 1755). Plant physiology1 Mfmoires pour servir d Vhistoire d'un genre de polypes d'eau douce (1744); cf.

J. R. Baker: Abraham Trembley of Geneva (London, 1952).


was studied by Hales with the aid ofquantitative physical methods

largely derived from Boyle (Vegetable Staticks, 1727). He measured

the upward pressure of the sap in the roots of plants, the quantityof water absorbed by the root and transpired by the leaves, and

the rate of growth in different structures. He proved that some

atmospheric substance entered into the composition of plants.

Such experiments he tried to elucidate mechanically by others on

the capillary attraction of water in fine tubes and porous sub-

stances; somewhat similar ones were extended to the circulation

of the blood in his Hamostaticks. Further important contributions

to physiology were made by the contemporary chemist-physiciansG. E. Stahl, Friedrich Hoffman and Hermann Boerhaave, whoalso continued a seventeenth-century tradition.

The physiological processes involved in reproduction and the

formation of the embryo, in particular, remained a matter for

heated controversy, on much the same lines as in the seventeenth

century. In J. T. Needham spontaneous generation had a new

champion, who found microscopic animalculae in boiled broth

that was (as he thought) effectively sealed from the air (1748). Hewas answered in more precise experiments by Spallanz,ani (1767),but this question was not regarded as decisively settled up to the

time of Pasteur. The great debate between Ovists and Animal-

culists was more widespread, and even less fruitful. Harvey hadbelieved in epigenesis, that is, that the growth of the embryoproceeded both by the gradual differentiation of its parts, and bytheir increase in size:

*

there is no part of the foetus actually in

[the egg], yet all the parts of it are in [the egg] potentially/ Theeffect of microscopy, soon after Harvey's death, was to giveimmediate advantage to the alternative theory of preformation,

according to which the embryo merely swelled from being aninvisible speck which was from the first completely differentiated;

as Henry Power said:' So admirable is every organ ofthis machine

ofours formed, that every part within us is intirely made, when the

whole organ seems too little to have any parts at all.' Preformation

was developed especially by Malpighi and Swammerdam. Since

the embryo, among oviparous creatures, develops in the maternal

egg, and microscopists believed that the first signs of its future

form could be detected as soon as the egg appeared, it was natur-

ally assumed by them that the embryo, or potential embryo, was

solely derived from the female. This view conveniently opposed


the unfashionable Aristotelean conception that the male, supplyingthe active "form/* was the prime agent in generation, and

the female responsible merely for the passive"substance

"of the

offspring. Aristotle seemed to be further confounded by the

discovery of the mammalian ovum attributed to De Graaf (1672).

This supposed discovery was premature De Graaf saw the

follicles since known by his name, and the true ovum was first

described by von Baer a century and a half later. However, it

brought about an essentially correct change of thought, to the

view that both viviparous and oviparous reproduction begin with

the fertilization of an egg formed in the female. According to

the Ovists, the ovum contained the embryo not potentially but

actually, and in the version of their theory known as emboitement

they supposed that this held within its own organs the ova of the

next generation, and so on ad infi'iitum like a series of Chinese

boxes: in the ovaries of Eve were confined the future forms of all

the human race.

The discovery of spermatozoa opened up a contrasting but

parallel theory. Leeuwenhoek, in one of his rare flights of hypo-

thesis, suggested that these "little animals" were the living

embryos, which were enabled to grow by transplantation into the

egg:'

If your Harvey and our De Graaf had seen the hundredth

part they would have stated, as I did, that it is exclusively the

male semen that forms the foetus, and that all that the womanmay contribute only serves to receive the semen and feed it.'

1 Hesupported this doctrine by reference to well-known cases where

the offspring ws strongly marked with the characteristics of the

male parent. Hartsoeker (1694) and Plantades (1699) the last

perhaps as a deliberate fraud published illustrations of a

"homunculus" enclosed in the head of a spermatozoon. Embotte-

ment was also taken up by the Animalculists in the eighteenth

century. Rival interpretations ofobservations that were commonlyvery imperfect and carelessly recorded continued for over a

hundred years. Some regarded the spermatozoa as products of

corruption, like the eel-worms in vinegar, for it was only in 1824that they were proved essential to fertilization by Dumas and

Provost; at about the same time the experiments of GeoffroySaint-Hilaire on the production of monsters proved that the

1 Letter to Nehemiah Grew, 18 March 1678. Collected Letters, vol. II,

(Amsterdam, 1941), p. 335.


appearance of the embryo is not preformed or predestined. At an

earlier date the scientist-mystic Swedenborg favoured epigenesis

(c. 1740), and more powerful support came from the researches

of Caspar Wolff at St. Petersburg (1768), who pointed out that,

as in plants the rudiments of flowers develop from undifferentiated

tissues and are at first undistinguishable from those of leaves, so in

animals no miniature foetus could be found in the earliest phaseofdevelopment, after which the nervous system, the blood-vessels,

and the alimentary canal were observed to arise in successive

stages. Generally speaking, however, the reaction against pre-formation (and the consequent expiry of the Ovist-Animalculist

controversy) did not occur until the close ofthe eighteenth century,

although, as F. J. Cole has said, the admirable iconography of

Malpighi carried its own refutation of its author's doctrines. 1

In most other branches of biology the eighteenth century

appears equally unproductive of truly creative investigation. In

its more medical aspects, such as human and comparative

anatomy, and human physiology, the successes of the seventeenth

century were extended, particularly during the last two decades.

Lavoisier, for example, was able as a result of his new theory of

combustion to throw fresh light on animal respiration. But the

greatest biological achievement of the period, that which won the

greatest fame and attracted the greatest number of pupils, was

certainly that of Carl Linnaeus (1707-78). His mastery of the

order of nature 'God,' as he complacently acknowledged, 'had

suffered him to peep into His secret cabinet' touched the imagi-nation of a generation already turning towards a romantic

naturalism, which was soon to cherish Gilbert White and Thomas

Bewick, to prefer landscapes to portraiture, and to talk contentedlyof the noble savage. Linnaeus was the prophet of Wordsworth.

His arrogance, like Samuel Johnson's, enslaved admiration, while

the confidence with which he wrote as though personally presentat the Creation was the more acceptable (in that, in all respects,

it reassured the somewhat conventional religious conscience of the

age) because it counteracted the scientific agnosticism of Voltaire

and the French philosophes. Most of the major advances of science

have, in one way or another, imperilled the comfortable securityof the popular understanding. One great merit of Linnaeus' in-

tellect was that, save in his great gift for classification, it was1 F. J. Cole: Early Theories ofSexual Generation (Oxford, 1930), p. 147.


remarkably undistinguished; he had neither the wish nor the

power to ipater les bourgeois.

That does not detract from the importance of his work. Linnaeus

was a sincere amateur of nature in all her moods; a competentteacher of many subjects in biology and medicine, able to inspire

affection and devotion in his students; a voluminous and lucid

writer. Like Newton, he possessed a strong, though not wholly

attractive, character. Like Newton too, he saw the essentials of a

problem and solved it. And he was only slightly less dominant

than Newton in forcing future naturalists to follow the path that

he had cleared.

The Linnean systems of classification embraced the animal, vege-table and mineral kingdoms, and even diseases. Of these the

second was by far the most complex, and the most influential. It

was derived by applying to the immense descriptive materials

amassed by Ray, Tournefort and others of his predecessors the

principle ofplant sexuality firmly demonstrated by the experimentsof Camerarius (1694). Thus plants were distributed into twenty-four Classes according to the number, proportions or situations of

the stamens (male organs), and each Class further subdivided in

accordance with the number of styles (female organs). The first

three Classes in this system were Monandria (i stamen), Diandria

(2 stamens), and Triandria; the Class Polyadelphia had "stamens

united by their filaments into three or more sets." In each Class

plants with one style were assigned to an Order named Mono-

gynia, those with two to the Order Digynia, those with three to

the Order Trigynia, etc. Each Order, easily determinable by in-

spection of the flower, contained a number of genera, which

groups Linnaeus regarded as primary and as "naturally" distinct.

Each genus had a brief description of the features common to all

the species included in it, mainly derived again from the methodof fructification. In further division into species the shape of the

leaves and other characteristics became important. For example,Genus 696 in Linnaeus

5

System ofNature is found in the Class Hex-

andria, Order Monogynia; it is called Berberis, and is distinguished

by "Calyx 6-leaved, petals 6, with two glands at the base of each,

style o, berry superior, 2-seeded." In this genus Linnaeus reportedfive species, one European, one Cretan, one Siberian, and twofrom Tierra del Fuego.The main principles of this classification apparently became


clear to Linnaeus at an early age, and were worked out with the

aid of the experience gained in the course of his journey throughLapland (

1 732) and during later European travel. The first version

of the System ofNature (1735) was written in Holland when he was

acting as botanical curator to Boerhaave. The illustrations of the

principles were extended vastly in the subsequent editions which

speedily issued from the press. (The tenth, of 1758, is now the

standard work of reference.) The utility of the work dependedvery much upon the rigidly methodical, and extremely succinct,

descriptions, which in turn were made possible by the use of a

technical terminology that was largely of Linnaeus' own creation.

He also paid great attention to nomenclature:

As I turn over the laborious works of the authorities, I observe thembusied all day long with discovering plants, describing them, draw-

ing them, bringing them under genera and classes: I find, however,

among them few philosophers, and hardly any who have attemptedto develop nomenclature, one of the two foundations of Botany,

though that a name should remain unshaken is quite as essential as

attention to genera.1

The rules which Linnaeus drew up for coping with this problem

anticipated in part those now accepted by international agree-

ment, and within a few years his binomial system was universally

accepted among naturalists.

The Linnean Order was determined by a purely mechanical

procedure. To it might be assigned thousands of different plants.

How were the further distinctions to be defined, and the lines

drawn between mere differences of variety, those of species, and

those of genus? Even post-Linnean taxonomy has not succeeded

in drawing such lines firmly, and in practice Linnaeus made muchuse of earlier experience. The concept of species is indeed some-

thing that can easily be grasped intuitively Aristotle had it in

perfect clarity for in very primitive languages the kinds of ani-

mals and plants are named even though the general concept

"plant" or "animal" is lacking. In surveying kinds of creatures,

it is not difficult to see why dog, wolfand hyena are more like each

other than any member of another group containing lion, tiger

and panther. The difficulty arises as the analysis of what consti-

tutes an effective likeness or unlikeness has to be made finer and

1 Critica Botanica, translated by Sir Arthur Hort, Ray Society (London, 1938) ;

Preface.


finer: should the wolf (which is interfertile with the dog) be placedin the same genus with the pekinese? Linnaeus realized that thoughthe species is the fundamental unit of taxonomy, the assignmentof the generic boundaries is the classifier's most tricky task. Here

he could offer no rigid rules, though he stated certain negative

propositions, and therefore his success was empirical rather than

theoretical. His system could be made to work, but because generic

groupings depended upon one man's notion of significant simili-

tude, it was far from infallible.

Although unable to define the characteristics of a species and a

genus precisely, Linnaeus did associate ideas with each of these

concepts that were received as dogmatic truths up to the time of

Darwin. Some had long been current without winning universal

credence. The most important of them was the fixity of species,

which Ray had not admitted. In Linnaeus' view each species

represented the descendants of an original entity, or pair of enti-

ties, individually created at the beginning of the world. Its flora

and fauna had always been exactly as they are now, and hence

the concept ofspecies was justified (if not, in practice, defined) bycommon descent from a unique created form, just as humanitywas defined by common descent from Adam. Equally, the disap-

pearance of species was ruled out, despite the evidence of fossils,

which were thus denied an organic origin.1

Until late in life Linnaeus regarded the production of fertile,

stable hybrids by crossings between members of the same genus as

impossible; intergeneric hybrids were unthinkable. Shortly before

1 760 new evidence led Linnaeus to believe that new species could

arise have arisen through differentiation by crossing. Perhapsafter all only the ancestors of the Orders were created but he

never perfected this thought, of which he seemed ashamed, and

though he withdrew from subsequent editions of the System ofMature confident statements that new species never occur, the

recantation came too late. It is strange that the chief legacy of

Linnean biology, the main scientific argument against Darwin, was

a doctrine in which the mature Linnaeus had himself lost faith. 8

1 Linnaeus was more orthodox than Steno, Hooke, Ray and others whoadmitted that living species represented only by fossilized shells, teeth or bonehad disappeared from the world, incompatible as this seemed with divine

Providence, and the care taken to preserve all the land-animals at the time ofthe Flood.

2 Cf. Knut Hagberg: Carl Linmtus (London, 1952), Chapter XII.


It is important to recollect that there was already, before the

end of the century, significant opposition to the doctrine of the

immutability of species. Evolutionary ideas were first applied to

the formation of the earth's crust, not its peopling with creatures.

Descartes and Leibniz, Burnet and Whiston, had each before 1 700devised an hypothesis to account for the separating out of rock andwater from an incandescent mass or primitive chaos, and traced

the depression of ocean-beds, the elevation of mountain ranges, to

the action throughout long periods of purely mechanical forces,

though the time-scale imagined was absurdly short. The first two

of these ignored the story of the Flood completely. Fossils, if ac-

cepted as organic remains, enforced the conclusion that species

had either changed, or disappeared. The great French naturalist,

Georges Cuvier (1769-1832), who founded the science of palaeon-

tology, favoured the second hypothesis. Successive catastrophesof which the Biblical Flood was the most recent had swept the

earth of life; successive creations had re-peopled it with new

species. His influence, more than any other, reinforced that of

Linnaeus in deriding evolutionary ideas, and in creating the in-

tolerant assurance in immutability which faced Darwin. But his

compatriot Buffon (1707-88), a man of less pretentious scientific

authority, whose main effort was directed towards descriptive

biology in the forty-four volumes of his Hisloire Naturelle (once im-

mensely popular, now a dead weight in booksellers' basements)chose the alternative explanation. For Buffon, as for Aristotle and

Ray, the living process became more complex by infinitesimal

gradations: 'Le polype d'eau douce sera, si Ton veut, le dernier

des animaux et la premiere des plantes.' The power to reproducein kind, and to grow, he regarded as the prime characteristic of

the living state. This power resided in "organic molecules," the

basic units of both plants and animals; death was the dispersionof these molecules, nourishment their assimilation into the bodyof the creature. Denying preformation in all its aspects, Buffon

asserted that the segregation of the"organic molecules" in the

sexual organs was the cause of reproduction, just as, in a different

way, it caused the generation of parasites. The organic molecules

had been the same since the beginning of the world; but, as he

stressed in his poques de la Nature, the world itself had altered,

evolved. In the Fifth Epoch elephants had roamed the far north;

the earth was hotter in its youth, and of greater vitality. Animals


were larger, witness the ammonites big as cartwheels, the hugetusks found in Siberia, perhaps even man was then a giant. In

general, Buffon imagined that the change in nature was towards

degeneration, but he was acute enough to see that where human

purposefulness had intervened, species had been changed for the

better. Bread-wheat, for example, was not a gift of nature, for it is

unknown in the wild state; it is evidently a herb brought to per-fection by man's care and industry.

* Our best fruits and nuts'

he

wrote,* which are so different from those formerly cultivated, that

they have no resemblance save in the name, must likewise be re-

ferred to a very modern date.' By selective breeding, man has 'in

a manner created secondary species which he can multiply at

pleasure.' Although, in such passages, Buffon appears as a no-

table precursor of Darwin, and although the fixity of species

(together with the taxonomical nicety attached to that doctrine)was alien to his mind, he made no great play with the idea of

evolution. It was not, for him, an explanatory concept. He did not

make it his task to account for the origin of specific differences.

Thus, in a variety of ways, the elements of modern biology grewout of the older natural history. Their growth was necessarily

spasmodic since it was not autogenous, the stages of the trans-

formation of the naturalist into the biologist being fixed by the

availability of techniques and ideas borrowed from physics, chem-

istry, medicine and philosophy. In the sixteenth century natural

history became a respectable branch of study; in the eighteenth it

was moulded into a formal discipline by Linnaeus; but the special

quality of the seventeenth century, which made biologists of menlike Harvey, Descartes, Hooke, Redi and Leeuwenhoek, who were

not naturalists, was the rich opportunity for opening up new sub-

jects, largely with the aid of imported methods. That the physical

science, and general intellectual climate, of the eighteenth centuryhad less in comparison to offer to the biologist was the chiefreason

for the failure of these new subjects to continue their startlinginitial progress.The distinction between natural history and biology is not, of

course, recent. Aristotle was a naturalist in the History of Animals,a biologist in the Generation ofAnimals. In the scientific renaissance,the writings of such an embryologist as Fabricius clearly fall into

a different category from those of Gesner. But the distinction is


one which the events of the nineteenth century finally made plain.

Through this perspective, a man who studies the courtship of

birds is certainly a naturalist; another who examines the differ-

ences between bird-blood and mammalian blood who may not

know a teal from a tern is as certainly a biologist. The naturalist

takes the whole rural scene for his province, and is primarilyinterested in creatures as individuals; the biologist is predomi-

nantly concerned to answer specific questions, and seeks generaltruths. The biological sciences are descriptive indeed, in the same

sense, however, that the chemical sciences are descriptive for

they use concepts like "genes," "evolution," "photosynthesis"which are as much the product of scientific inference as

"atom" or "polymerization." Natural history, on the other hand,"describes" in the commonplace sense of the word; its conceptslike "mating," "hunting," "feeding young" are those of ordinary

thought, rarely the product of scientific inference. The naturalist

is indeed a trained observer, but his observations differ from those

of a gamekeeper only in degree, not in kind; his sole esoteric

qualification is familiarity with systematic nomenclature. 1

Natural history, as here differentiated from biology, seems at

the present time to be ofsmall and shrinking scientific significance.

The naturalist has inevitably become dependent upon the deeper

insight of the biologist so that (for example) questions of classifi-

cation, after being his main concern since the sixteenth century,have been radically modified during the last hundred years bybiological research into evolution and embryology. The introduc-

tion of new and more rigorous techniques, making large use of

the experimental method, has carved from the naturalist's former

province such subjects as ecology and animal psychology. In anycase, the observations of a Gilbert White are no more repeatablethan those of a Marcel Proust, and partly for the same reason that

their enduring interest resides in individual qualities of imagina-tion and literary skill applied to a particular social setting. The

writing ofnatural history may continue, like that of the novel, ever

different and ever the same, but the evolution from it of scientific

biology could only happen once (or, more accurately, in successive

1 These distinctions are, it is recognized, subject to innumerable qualifica-tions. In practice, many biologists share the naturalist's attitude in part, andmany naturalists the biologist's; more exact experimental methods are bringapplied to field-work, etc.

3oo THE SCIENTIFIC REVOLUTION

unique stages) just as the science ofpsychology could only emergeonce from the physician's interest in mental disorders.

The emergence of biology was certainly the leading contribution

of the scientific revolution to the study of living things. A totally

new kind of knowledge was thereby made possible, supplementaryto that already obtained through the renaissance of natural

history in the sixteenth century. Necessarily the first steps in this

emergence were mainly descriptive, in studies of comparative

morphology, minute anatomy and physiology, and the like. The

description of an animal or plant which permits its identification

may, however, be very different from a description of the samecreature in relation to an appropriate group of scientific in-

ferences. The structure of the hoof and leg of the horse may be so

depicted, or portrayed in words, that the member may be easily

distinguished from that of a dog; but to describe the same leg of

the horse in terms of its evolution by extension of the middle digit

of the foot and reduction of the side-digits is to embark upon a

very different procedure. Or, to take an example from mineralogy

(since this was a part of natural history until recent times) whenmetallic ores have been classified and labelled under such namesas malachite, chalcocite or chalcopyrite, a new kind of knowledgeis brought in by assigning to them their appropriate chemical

formulae. Though these formulae are merely descriptive of the

composition of the minerals, they enable comparisons to be madewhich are otherwise hidden.

A mineralist who considers gypseous alabasters, plaster stone, lamel-

lated gypsums, . . . and a great many other bodies as proper to be

distinguished from one another, and who is able to ascribe anyparticular body to its proper species from considering its external

appearance, is possessed of a particular kind and degree of know-

ledge: He who besides being acquainted with the external appear-ances, is able to prove that all these different bodies are composed of

a calcareous earth, united to the vitriolic acid; and thus makes several

species of things coalesce together, and unite, as it were, under one

general conception, hath a knowledge of these bodies different in

kind and superior in degree.1

In the former example, appeal was made to the concept of

evolution, in the latter to the concepts of inorganic chemistry.

1 Richard Watson: Chemical Essays, vol. V (London, 1787), p. 127. Cf.

L. J. M. Colcby in Annals of Science^vol. IX (1953), p. 106.


But the naturalist's description is sui generis, and all its complexityis no deeper than that of an unfamiliar vocabulary.At the close of the eighteenth century many of the procedures

followed by the biologist in the course of his still mainly descriptive

work as one may see from the investigations of Cuvier, of Haller,

of Lavoisier, of John Hunter already anticipated those of the

twentieth century. They were at least as "modern," by the same

comparison, as those of the contemporary physicist and chemist.

The great change has taken place in the intellectual framework

within which such procedures are ordered. Biology had, indeed,

successfully constructed an unco-ordinated group of scientific

inferences, but it was still devoid of basic guiding principles: or

rather, those which it possessed were derived from extra-scientific

sources. Comparable in this state to mechanics before the seven-

teenth century, the extent and the accuracy of the observational

material collected together was by 1800 far greater. The science

had followed a rather haphazard Baconian course, for althoughinformation had been compiled piecemeal with great diligence,

the elucidation from it of keys to the understanding of livingnature had hardly begun. The "laws of nature" were as yet

purely inorganic: all the great theoretical principles of biologyhave won their dominion during the last century. This being so,

it may be recognized that the chief difficulties confronting

biologists during the critical period 1750-1850 that in whichthe influence of the natural-historian Linnaeus was at its heightwere those of conceptualization; as, again, had been the case in

mechanics long before. The possibilities for significant theoretical

thinking open to men who accepted the futilities of embottement or

the doctrine of successive catastrophes were as limited as those

available to the Aristotelean opponents of Galileo.

The similarity ceases, however, when the intrinsic difficulty of

establishing the "laws" of biology is compared with that of

clarifying the "laws" of mechanics. More mental effort is requiredto grasp the necessity for the concept of evolution than to see the

plausibility of that of inertia; more important, it is possible to

justify the former only by elaborate discussion of varied and

obscure evidence. Darwin's Origin of Species has a very different

character from Galileo's Discourses on Two New Sciences. Darwindevoted more than twenty years to the filling of note-books with

materials bearing on his problem, materials which were in part


made accessible to him by a long tradition of descriptive natural

history, and which owed much to the taxonomical precision of

his authorities. He was himself an expert taxonomist. 1Similarly,

the elements of the cell-theory were pieced together as the result

of an even greater mass of cumulative observation, extending to

the seventeenth century. The principles of biology could not

spring from the analysis of common and simple observations, as

did those of mechanics; and although it may truly be said that

much current research owes little directly to the tradition of

classificatory refinement stretching through and beyond Linnaeus,

its origin lies in descriptive work to which that refinement was

essential. A novelist does not need to be a lexicographer, but

dictionaries are an essential foundation of good literature.

Although biology has emerged from the natural history stage, its

methods are not, and perhaps can never be, identical with those

ofphysics. However great its development within laboratory walls,

it must always have room for those techniques of description anddiscrimination with which the naturalists of the sixteenth centuryfirst strove to create a science.

1 One reason for undertaking his monograph on the Cirrepedia (1851) wasto prove to himself (and the world) that he was no mere philosophical biologist;

though he afterwards doubted * whether the work was worth the consumptionof so much time.'

CHAPTER XI

THE ORIGINS OF CHEMISTRY

CHEMISTRY,

as an integrated science with its own concepts,its own techniques, and its own area of applicability, is a

product of the scientific revolution. The ancients, and their

medieval successors, had no such distinct science, though theyhad much scattered empirical knowledge of this type, and sometheoretical ideas that would now be described as of a chemical

nature. Alchemy was not a primitive or pre-scientific chemistry,for it was both less (in the restricted range of its pretensions) andmore (in its mystical affiliations) than a natural science. Chem-

istry, like biology, grew from a number of distinct roots, andnot by the expansion of a single tradition, as did mechanics and

astronomy. Hence the attempt to classify the sources of chemical

knowledge and theory in the early modern period becomes

complex, and shows that these had little relation to the sub-

divisions which now prevail. Researches of chemical significanceoccurred in mineralogy, in physiology, in physics, in pharma-cology, and most obviously in the development of technology.

Likewise, the concepts used by writers on chemistry before the

time of Lavoisier were often common property among natural

philosophers, rather than exclusive to their own science. Such is

the case with the four-element theory of matter, and with the

corpuscularian "mechanical" hypothesis; both were physical, or

rather cosmological, in origin. Chemistry, again like biology,shows that a science gains stature as it acquires its own specialized

concepts as instruments of thought. Stage by stage, from the theoryof the three principles in the sixteenth century, through that of

phlogiston to the Lavoisierian notion of the chemical elements

and their combinations, the science developed coherence and

independence.Hence the idea that there is a particularly chemical way of

studying matter and its properties, whether inorganic or organic

matter, was almost totally absent before the late sixteenth century,and even then gained ground but slowly. Early speculations about

303


the nature or composition of matter, and about the processes

involved when one kind of stuff is turned into another kind of

stuff, were a part ofphysics, as little empirical as the rest ofphysical

theory. They were scarcely at all connected with the practical

knowledge of certain groups of craftsmen. In a similar mannerit was far from obvious that a distinct science was required to

explain how the bread that man eats is transmuted into flesh and

bone. A pre-scientific physiologist might speak of "concoction"

in the stomach, but the term, though frequently used by chemists,

had no specific meaning. It was an empty word that described

nothing and explained nothing. When, however, certain experi-

menters adopted the belief that all metals are variously com-

pounded of sulphur and mercury using the names sulphur and

mercury in a particular sense distinct from that of ordinary

language it does become possible to speak of a chemical attitude

to substance. Robert Boyle frequently applied the word "chymist"in this way, as describing those who thought and worked in

accordance with the three-principle theory. Otherwise the

chemist was only distinguished from other men by the nature of

his methods: 'What is accomplished by fire/ wrote Paracelsus,

'is alchemy whether in the furnace or in the kitchen stove.' 1

The chemist was indeed primarily a pyrotechnician, who knew (or

tried to discover) how to obtain certain results by long and gentle,

or short and fierce, heating. To the end of the seventeenth centurychemical analysis was practically confined to destructive distilla-

tion by fire, in which the substance to be analysed was forced to

yield its waters, oils, sublimates, salts and caput mortuum. In this

sense the metal-refiner, the soap boiler and the distiller were

chemists; the practices of more learned men in the early modern

period were hardly less haphazardly empirical than theirs, andowed little more to the guiding influence of a distinctive theory.

And, as chemical ideas were but slowly differentiated from those

generally current in natural philosophy, so chemical techniqueswere very gradually differentiated from those of the kitchen and

workshop. Even in the time of Lavoisier they still bore strongmarks of their craft origin.

Two possible approaches to the early history of chemistry

are, therefore, bound to prove misleading, and to conceal the

1 Alchemy to Paracelsus meant something much wider than the search for

the secret of the transmutation of base metals into gold.

THE ORIGINS OF CHEMISTRY 305

significance of the development of the science during the period of

the scientific revolution. It is futile to attempt to trace the progres-sive evolution from primitive beginnings into a modern form of

a texture of chemical theory, because the idea that it is useful to

apply a group of characteristically chemical concepts to the studyof nature is itself modern. It is equally futile to derive chemistryfrom the elaboration of certain techniques of investigation, firstly

because it is doubtful whether these enabled useful empiricalfacts to be discovered before a late date, and secondly because the

intellectual background to the refinement of technique is far more

significant than the refinement itself. If modern chemistry is not,

as mechanics is, the result of the progressive emendation of an

autogenous conceptual structure, it is also not that of purelydeductive reasoning applied to

"natural history" information

collected about the properties of minerals, acids, alkalis, etc.

though this view seems to contain more truth than the former. Onthe other hand, two analogous questions may usefully be asked.

What attempts were made to account for changes in the propertiesof bodies effected by various manipulations (mainly with the aid

of heat) in the light of existing scientific theory? How successfully

were techniques adapted or invented with the double object of

advancing technology and understanding? By asking questions of

this form it is possible, without plunging into confusion, to

recognize the indubitable facts that chemistry was always an

eminently practical science, as well as a branch of natural

philosophy, and that it lacked (before Lavoisier) a coherent

conceptual scheme.

To state the problems in such terms is not to deny that theoryand practice were interdependent, or that individual chemists like

Boyle might both add to factual knowledge, and seek for an ex-

planation of chemical phenomena in current scientific thought.It does, however, admit that these two strands in the history of

chemistry are logically distinct. This is very clear in the late

medieval period. Then, natural philosophers were engaged in try-

ing to fit the known facts of chemical change into the pattern of

Aristotelean ideas concerning the nature and properties of matter,

exactly as, more assiduously, they tried to arrange the facts of

physics and astronomy according to the same pattern. Meanwhile,the pattern itself preserved its character, and no essentially newideas were brought out. By contrast, empirical knowledge of the

3o6 THE SCIENTIFIC REVOLUTION

phenomena ofchemistry increased rapidly during the same period,

owing progressively less to a remote Hellenistic ancestry. In glass-

working, in the smelting and refining of metals, in dyeing and

leather-dressing, in military pyrotechnics, in the distillation of

alcohol and other "waters," in the glazing of pottery and the

preparation of pigments generally, in the manufacture of medica-

ments of all kinds briefly, in every aspect of chemical technologythe European world of about 1500 enjoyed a consistent superiority

over the Graeco-Roman. In the millennium between the fall of

Rome and that of Constantinople alcohol and the mineral acids

were discovered, saltpetre was distinguished from soda (this made

gunpowder possible), many new minerals were recognized,

named, and their usefulness exploited, the known compounds of

metals increased in number, chemical apparatus assumed a defi-

nite form, the control of furnaces was improved, and operationslike reduction and oxidation were mastered (though their nature,

of course, remained unknown). Some of this knowledge emanatedfrom a Graeco-Egyptian tradition, centred on Alexandria; im-

portant elements were derived from India and China, but prac-

tically nothing came from the academic scientific line of the

ancient world, stemming from Plato and Aristotle through Pliny.

The whole was synthesized and further advanced by the Islamic

peoples, who were excellent chemical craftsmen, and further con-

siderable progress was made in the Latin West from the twelfth

century onwards. As some of the important sources, such as the

writings of Geber and the Book of Fires of Marcus Graecus, are

now accredited to Latin compilers who made use (to a degreewhich cannot be exactly estimated) of unknown originals, the de-

tailed ascription of inventions in the chemical arts to Byzantium,

Islam, or Latin Europe is often impossible. But it is quite certain

that they are post-classical.

Little reflection of this growing empirical knowledge is to be

found in the writings of medieval natural philosophers, with the

rare exception of Roger Bacon. Only such discoveries as were

possibly effected, or alternatively adopted, by the alchemists (like

the preparation of mineral acids and the solution of metals in

them) were of interest. More was done by physicians, with regardto pharmacologically useful discoveries. The third class of writingwhich gives an insight into medieval chemical technology consists

of recipe books of many types, among them the different versions


of the Mappa clavicula, the Note on various crafts of the monk Theo-

philus (c. 1200), the Book ofFires already mentioned, and the Book

on colour making of Peter of St. Omer (c. 1300). This class becomes

much fuller from the fourteenth century. While, therefore, texts

in this group may be drawn upon to form a picture of the level of

factual knowledge concerning the preparation and properties of

substances attained by the close of the middle ages, it is almost

useless to look to them for the beginnings of a chemical attitude.

The literature of alchemy is copious, and many have searched

in it for the beginnings of chemistry. There the grain of real know-

ledge is concealed in a vast deal of esoteric chaff. The view that

alchemy represents the pre-history of chemistry (as developingchemical techniques, and factual knowledge ofsubstances) is, after

all, primarily based on the fact that such information is frequentlyset out, in the surviving texts, in an alchemical context. But there

is no means ofknowing that, because a discovery or an observation

is first reported by an alchemist, it was made as a result of his

inquisitive experimentation. The most remarkable feature of all

alchemical writings is that their authors prove themselves utterly

incapable of distinguishing true from false, a genuine observation

(according to our modern knowledge) from the product of their

own extravagant imaginations. It seems unnecessary to give themcredit for making important truths known, when they were so

obviously incapable of discrimination. It is certain that manypractices and observations of alchemy were older than alchemyitself, just as observational astronomy preceded astrology. It is also

certain that in the medieval period much knowledge was gainedoutside the alchemical context which was restricted, almost ex-

clusively, to metallic compounds. Taken together, these facts

suggest that were the early history of practical, industrial chem-

istry more fully revealed, the inventiveness attributed to the

alchemical dream would be found exaggerated. Some of the dis-

coveries attributed to it may well have come from a differently

directed experimentation; some alchemists were also physicians.The theoretical contribution of alchemy to science was very

small. Its own pretensions forbade the application of the usual

notions of natural philosophy to the phenomena studied, and

despite the interest of some philosophers in the art, there were

always others who derided it. The theory of transmutation held

by the later alchemists was originated by Jabir ibn Hayyan and

3o8 THE SCIENTIFIC REVOLUTION

al-Razi. It was made known to Europe in the twelfth century.

They believed that all metals are composed of "philosophic"

sulphur and "philosophic" mercury, which could be obtained byart from the base metals, and recompounded to form the preciousmetals: 1

Therefore if clean, fixed, red, and clear Sulphur fall upon the pureSubstance of Argentvive (being itself not excelling, but of a small Quan-

tity,and excelled) of it is created pure Gold. But if the Sulphur be clean,

fixed, white and clear, which falls upon the Substance of Argentvive,

pure silver is made . . . yet this hath a Purity short of the Purity of

Gold, and a more gross Inspissation than Gold hath.2

It is enough to say that this theory was never developed (save in

mystical embroidery), that it was never attached to any sound

body of empirical knowledge, and that its persistence was the

greatest obstacle to the development of a rational chemistry.In any case, the pursuit of alchemical chimaeras had long ceased

to bring any useful information to light by the beginning of the

sixteenth century. The significant event of this time was the

emergence, from the obscure and laconic notes of recipe-books, of

literate descriptions of the operations of chemical industry, espe-

cially those connected with metallurgy. These books have been

discussed already (pp. 221-3). Here at last was metallurgical

chemistry (and much more) free from the extravagances of al-

chemy. Here was a clear discrimination between fact and fiction

with regard to the "transmutations" effected by chemical art.

Theoretical speculation was almost entirely absent from these

accounts, Agricola alone being notable for an attempt to explainhis observations in terms ofAristotelean science, without, however,

improving its texture. Thus was founded a serviceable and lasting

tradition, which after a recession lasting through a couple of

generations (those most subject to the influence of Paracelsus) was

again revived by the scientific societies. From that time the

academic study of industrial chemistry was never neglected.

Eighteenth-century chemists like Black and Macquer were closely

associated with it. Lavoisier did an enormous amount ofwork as a

government consultant, reforming the administration and chem-

1 These principles were ultimately compounded of the Aristotelean ele-

ments, but could be procured, as it were, as intermediate states.1

Argentvive = mercury. Works of Geber, Englished by Richard Russell 1678.Ed. by E. J. Holmyard (London, 1928), p. 132.


istry of the French explosives industry. And it may safely be said

that the rapid extension of chemical research in the nineteenth

century and later would have been impossible but for its close

connection with manufacture. Much earlier the remarks of the

Fellows of the Royal Society, especially Robert Boyle, on the

necessity of close attention to trade methods give a hint of a source

from which much was learnt not least, in the way of suggestingthe type of problems which might most usefully be attacked. For

on this, it is obvious, modern chemistry largely depended for its

early success. The only problems which the early chemist could

hope to solve in a rational way were the simple ones dealing with

the oxidation of metals, the calcination of limestone, quantitative

analysis of simple inorganic compounds which were in fact posed

by the basic chemical industries. However stimulating the fascin-

ating questions suggested by more elaborate chemical changes

might be, including those raised by the krown connection be-

tween chemistry and medicine, answers to them remained far

over the horizon until such time as organic chemistry slowlyincreased its scope through the mastery of inorganic reactions.

Though the endeavour to render physiology a branch of chem-

istry inevitably failed in the sixteenth and seventeenth centuries,

nevertheless it did on the one hand promote the development of

a distinctively chemical attitude to physiological and other prob-

lems, and on the other led to extensive exploration of chemical

compounds with the object of using them as drugs. Inorganicmedicaments were not new. Salt has always been collected as a

necessity for life; antimony sulphide, copper salts, sodium carbon-

ate, ochres, alum, and other minerals are prescribed for various

purposes in the Papyrus Ebers (sixteenth century B.C.).1Possibly less,

and certainly not greater, faith was attached to them in late

medieval Europe. These were, however, natural substances, not

the factitious products of art, few of which had yet been identified

with naturally-occurring minerals.

Roger Bacon had taught that medicine should make use of

remedies provided by chemistry, but it was not until the sixteenth

century that his idea was fully developed, by TheophrastusBombastus von Hohenheim (1493-1 541)* called Paracelsus, the

founder of iatrochemistry (medical chemistry). His was not in

any sense a modern mind. He believed in the philosopher's stone.

1 H. E. Sigcrist: History of Medicine yvol. I (Oxford, 1951), p. 343.

3 io THE SCIENTIFIC REVOLUTION

He believed in the alchemical theory of transmutation, and in

others yet more wonderful:

If the living bird be burned to dust and ashes in a sealed cucurbite

with the third degree of fire, and then, still shut up, be putrified with

the highest degree of putrefaction in a venter equinus so as to becomea mucilaginous phlegm, then that phlegm can again be brought to

maturity, and so, renovated and restored, can become a living

bird. . . .*

He had in full measure the faculty for self-deception characteristic

of the Hermetic tradition. For him, the physician and chemist

were one, a magus whose operations influenced the natural and

supernatural worlds together. In the words of Lynn Thorndike:

for Paracelsus there is no such thing as natural law, and consequentlyno such thing as natural science. Even the force of the stars may be

side-tracked, thwarted or qualified by the interference of a demon.Even the most hopeless disease may yield to a timely incantation or

magic rite. Everywhere there is mystery, animism, invisible forces. 2

But he was an iconoclast. He poured scorn upon the revered

writings of Galen and other authorities. For their dietary rules andherbal preparations he wished to substitute new drugs purified bythe action of fire. 'The work of bringing things to their perfectionis called alchemy, and he is an alchemist who brings what nature

grows for the use of man to its destined end.' Vulcan was to be his

apothecary. In his medical practice he made much use ofchemical

preparations of herbs (to extract their virtue), laudanum, alcohol,

mercury and metallic compounds, obtained by techniques familiar

to alchemists. In theory, he added salt to the other alchemical

principles, sulphur and mercury; otherwise his theoretical notions

were fully as chaotic as those of other alchemists.

No great reformation was to be expected from Paracelsus' in-

coherent, obscure, megalomanic writings. Yet the iatrochemical

school flourished; the greater part of what was done up to Boyle'stime may be attributed to it, and during two generations chemists

were to a greater or less degree Paracelsians, known by their

attachment to the three principles. Indeed Paracelsus' theses with

1 A. E. Waitc: Hermetical and Alchemical Writings ofParacelsus (London, 1894),VOl. I, p. 121.

fHistory of Magic and Experimental Science, vol. V (New York, 1941), p. 628.


regard to medicine, that useful drugs could be made in the labora-

tory, and that there was room for bolder experiment in the treat-

ment of disease, were obviously correct when purged of the

fantasies and occultism with which, in him, they were alwaysenmeshed. No one could doubt the efficacy of Glauber's sal mirabile

(sodium sulphate), and long before Paracelsus' time the adminis-

tration of mercury had been proved a specific against the commonand dangerous disease, syphilis.

1 The ambitions of the iatrochem-

ists were to reveal the chemical nature of physiological processes,

by discovering the secret laws by which the combinations and

recombinations of matter are governed, and to enlarge the list

of compounds known to be effective against disease. These were

rational objects, though the manner in which they were pursuedwas haphazard. Paracelsus had done little in chemistry himself. His

successors devoted themselves more fully to mastering the tech-

niques which would yield hitherto unknown substances. They did

not hesitate to draw, where they could, upon the experience of

industrial chemistry.These men were the "chymists" or "spagyrists" known to

Boyle and his contemporary philosophical chemists. They were

men of learning and wrote Latin. Their view was narrow, beinglimited by the doctrine of the three principles, and they were

often subject to the delusions of alchemy, but their books were

meant to be understood. They created no secret language.Instead they began to describe, as plainly as their knowledge and

terminology allowed, how the operations of chemistry are per-

formed, from what materials and by what methods a large numberof compounds are prepared, and for what purposes they might be

employed. They began to compare the method used in one case

with that used in another, to detect analogies between different

compounds, and to try to explain what happened when a chemical

reaction occurred by means of concepts which they invented or

adapted. Here was the beginning both of a"natural history" of

chemistry, and of a chemical theory.Andreas Libavius (d. 1616), the first important iatrochemist

1 Salivation was condemned by many non-iatrochemical physicians,because death was so often caused by mercurial poisoning. Medical faculties

forbade the use of iatrochemical methods for well over a century, Sir Theodorede Mayernc, James Ts physician, being expelled from Paris on this account.

They were gradually admitted to official pharmacopoeias during the seven-teenth century.

3ia THE SCIENTIFIC REVOLUTION

after Paracelsus, refused to number himself among the latter's

followers. From his Alchemia (1597) he claimed, justifiably, to

have omitted the magical and superstitious elements introduced

by Paracelsus, and to have purified the art of his figments and

phantasms.c

Unhappy would chemistry be, if it had been founded

by Paracelsus. . . . Filthy are the Paracelsian lies and blasphemies.'

Nevertheless, he still believed in transmutation. The Alchemia was

Libavius5 most important work, though he admitted that it was

largely compiled from other writers. 1 It is a methodical account

of the chemical knowledge and laboratory technique of his time.

He described many antimonial and arsenical compounds,2 sul-

phurous acid, the stannic chloride (SnCl4 )known as "Libavius'

fuming liquor," the extraction of many oils, waters and essences,

and the analysis of mineral waters. In the second edition there

is a long discussion, with wood-cuts, of the design of a chemical

laboratory. From such a work as this it was but a step to the

treatment of chemistry simply as an auxiliary of medicine. This

is the attitude of Jean Beguin in his Tyrocinium Chymicum (1610)who thus defined his subject: 'Chymistry is the Art of dissolvingnatural bodies, and of coagulating the same when dissolved, and

of reducing them into salubrious, safe, and grateful medicaments.'3

The Tyrocinium is a very straightforward recipe book, forerunner

ofmany others ofthe same kind.

The greatest of the iatrochemists, Johann Baptista van Helmont

(1577 or 1580-1644) was a figure in some ways only less flam-

boyant than Paracelsus, for he also gave his imagination free

licence. His criticism of academic medicine was more reasoned

than Paracelsus', but not less severe. 'The art of healing,' he

thought, "was a mere imposture, brought in by the Greeks. . . . Tothis day the schools do scarcely acknowledge any other remedies

than blood-letting and their stock of laxatives; their whole

endeavour is with bleeding, evacuations, baths, cauteries, sweats,

so that they presume to cure all ills of the flesh by weakening the

1 There are two editions, Alchemia Andrea Libavii Med. D. Poet. Physici

RoUmburg, etc. (Frankfort, 1597), p. 424; and the large folio with wood-cuts

Alchymia Andrea Libavii, recognita, emendata, et aucta etc., (Frankfort, 1606),

pp. 196 + 402 -f 192.2This, of course, was before the Triumphal Chariot ofAntimony of the pseudo-

Basil Valentine.3

Tyrocinium Chymicum 9 or Chymical Essayes Acquired from the Fountaine ofNature and Manuall Experience [trans, by Richard Russell] (London, 1669), p. i.

This primer was deservedly popular.


body and its strength, and by corrupting the blood.' 1Despairing

of such methods, van Helmont turned to chemistry because

insight into nature generally, and the workings of the human bodyin particular, could only be gained through a sound knowledgeof substance. To this end he developed a totally novel theory bywhich he proved himself far more than a mere chemist like

Libavius. In the first thirty chapters of the Ortus Medicine he

sketched out a new natural philosophy, often obscure and

muddled, and more than tinged with a naive credulity, which

was as much directed against Aristotle as against Galen. His

speculations ranged far beyond the bounds of chemistry and

medicine, to meteorology and the causes of earthquakes. Themost important of them was his contention that there are onlytwo elements, Air and Water. Fire he did not regard as a body,and therefore it could not be an element. All solid bodies, includ-

ing the earths, were generated from water by the action of seeds

or ferments:?The first beginnings of bodies, and of corporeal

causes, are two and no more. They are surely the element Water,from which bodies are fashioned, and the ferment by which theyare fashioned.' 2 These divinely created ferments were the specific

organizers of water, the prima materiayinto minerals as well as

living things; they were immaterial, though the seeds to which

they gave rise were not. Van Helmont referred in support of this

doctrine to the success of chemists in reducing solid bodies to

an "unsavoury water" (e.g. by solution in acids, followed byneutralization); to the fact that fishes are nourished solely onwater (!); and to his famous experiment on the growth of a

willow tree in a tub of earth. Although nothing but water was

added, the tree gained 164 Ib. weight in five years without anydiminution of the earth in which it was planted; water had

clearly been transmuted into solid matter by the action of the

"seed" in the tree.3 Like Boyle later, van Helmont attacked the

three principles of orthodox chemists on the ground that somebodies could not be resolved into them. He accepted the existence

of vacua in solid matter: for this explained how metals could be

1 Ortus Medicin*, Col. I, 6; III, 7. This collection of all van Helmont'sworks was published by his son at Amsterdam in 1648. An English translation

by John Chandler appeared in 1662.9 Ortus Medicina (Lyons, 1667), p. 23.8

Ibid.) p. 68. The experiment had been suggested by Nicholas of Cusa in the

fifteenth century.

3 i4 THE SCIENTIFIC REVOLUTION

more dense than water. Air, however, could not be turned into

water, even by great compression, and was therefore a distinct

element.

False thinking on these matters was, in van Helmont's view, the

main cause of error in science down to his time. He also attached

great importance to two new conceptions, for which he coined

new names. One was "Bias" a sort of intrinsic motion in the

stars and planets (which thereby affected the earth beneath), in

the air, and in man. The other was "Gas," which name had

a significance quite other than that now attached to it. VanHelmont's gas was simply a form of water, and he used the idea

to confirm further his theory that water was the prima materia.

Any matter, such as water vapour, carried into the extreme upperair, was turned into gas (i.e. was finely divided, since 'gas is far

more subtle than vapour, steams, or distilled oils, although muchdenser than air') by the sharp cold and the "death" of the

ferments. Then this gas might itself condense into vapour and fall

as rain: at any rate, it was the chief cause of meteorological

phenomena. Again, when substances burnt, the greater part of

them disappeared as gas, which was also water, or*

water

disguised by the ferments of solid bodies.' The point of vanHelmont's observation, that there is only i Ib. of ash obtained

from 62 of charcoal, the rest disappearing as spiritus Sylvester (wild

spirit), seems to be that the charcoal itself is gas, i.e. water. 1

He knew that if the escape of the spirit was prevented, by en-

closing the charcoal in a sealed vessel, combustion would not

occur. This led him into his celebrated definition: 'This spirit,

hitherto unknown, which can neither be retained in vessels nor

reduced to a visible body (unless the seed is first extinguished) I

call by the new name Gas. 92 Thus van Helmont's element-theory

might be symbolized

water + seed (ferment) > substance

and with his concept of gas this became

water > vapour * gas > water,

and (water + seed) > substance * gas v water

1 He had already "proved" that ash could be turned into water.8 Cf. Ortus Medicina

"Progymnasma meteori," "Gas aquae," "Complexio-

num atque mistionum elementalium figmentum."


In other words, the concept of gas was simply a complexity addedto the doctrine which van Helmont most wanted to drive home,that is: water is all. Its main function was to explain the otherwise

rather awkward fact that the products of combustion do not

normally include much water-vapour. Just as he had to denycorporeal status to flame and fire (which could not be supposed to

come from, or turn into, water) so van Helmont had to invent

gas as a form of water.

He noticed that gas might be evolved from a combination of

substances, or a substance acted upon by a ferment, though not

if the substance was taken by itself. Thus he found that saltpetre

alone yielded no gas, but that gunpowder does hence the violence

of the explosion. Grapes yielded a gas when bruised and fermented.

He also applied the name gas to the red fumes given off whennitric acid reacts with silver, to the product of the reaction between

sulphuric acid and salt of tartar, to the fumes given off by burning

sulphur, to flatus, to the poisonous substance which collects in

mines and extinguishes candles, etc. While unable to recognizeand classify these different gases systematically, he was of course

able to make qualitative distinctions between nitric oxide, sulphurdioxi' e, carbon dioxide, mixtures of hydrogen and methane, andthis particular attention to

" fumes" (which must have been veryoften observed in the past) was perhaps van Helmont's best

service to chemistry. But there is no evidence that he ever ad-

vanced beyond the notion that gases were substantially water,

modified by the characteristic of immaterial ferments: indeed, he

does not seem to speak of"gases" at all, as a plurality.

It has often been said, and rightly, that the long failure to

understand the role of the common gases was a grave obstacle

to the development of chemistry. It seems, however, that van

Helmont, despite the praise frequently meted out to him as the

first student of gases, really did little to lessen this obstacle. Themodern notion of gas involves two propositions, the second being

logically unnecessary, but required by experience: (i) There is a

state of matter in which the particles are separated and free to

move, rendering the matter tenuous and elastic; (2) Some forms

of matter are normally encountered only in this state. Now the

first of these propositions, though it was little developed theoretic-

ally before the nineteenth century (having been disregarded, for

the most part, by the practical chemists who really worked out


something of the importance of gaseous elements in chemical

combinations) would not have seemed at all unfamiliar to

seventeenth-century physicists, to whom the particulate nature

and elasticity of "airs" were commonplaces. Their notions of

"factitious airs" and "elastic fluids" clearly foreshadowed the

modern physical idea of a gas. But they had no correspondingchemical conceptions. The pivotal discovery, the apprehension that

made Lavoisier's chemistry possible, was the enunciation of the

second proposition in a chemical setting. It was the fact that some

participants in chemical reactions both elementary and com-

pound could normally be isolated in the gaseous state only,

though capable of entering into solid and liquid combinations,which was of strategic significance.

Therefore van Helmont's view of gas as a state of matter

intermediate in fineness between a vapour and the element air,

and as the fume, smoke or spirit evolved from a chemical process,

was ofvery little profit in itself. While his ideas helped to encourageinterest in these curious products, there was little real merit in

the attachment of a special name to something so vaguely con-

ceived, and so deeply involved in an unacceptable doctrine of

watery transmutations. Chemists especially the English con-

tinued to speak of "airs" and "elastic fluids" with good reason;

they chose rather to believe that gases were modified air than (withvan Helmont) that they were modified water, and air an inert

element. It cannot be said that they preferred the less plausibleof the two hypotheses. To have converted the Helmontian view

"gas is a state of water" into the statement "gas is a form of

material substances, distinct from air, which participates in

chemical reactions" was impossible. If van Helmont was right

(as we now know) in suggesting that gas is not air, it was far moreobvious to contemporaries that he was wrong in maintaining that

gas was a phase in water > substance > water transmutations.

Chemists like Boyle could make nothing of his Gas and Bias.

They could not see that of these two whimsical notions, the former

was far more worthy, since to them the single-element doctrine in

which van Helmont's gas is involved was incomprehensible. Evento hint that the subsequent neglect of van Helmont's work on gasretarded the development of chemistry is to misunderstand the

content of his thought, and to convey a thoroughly misleading

impression.


About the middle of the seventeenth century the position in

chemical theory (to use what is still an anachronism) was that the

Aristotelean doctrine, now moribund and opposed to the broadtrend of the scientific revolution, was still respectable; practising

chemists, as a class, stood by their three principles and the generaltenets of iatrochemistry; van Helmont's single-element theoryaroused much interest, but won few adherents. Meanwhile, a

fourth approach to the problems of chemical combination, based

on the mechanical, particulate view of matter was taking shape,and was soon to be developed elaborately by Robert Boyle.Factual knowledge of chemical reactions and processes had also

ramified considerably since the time of Libavius. Van Helmont

himself, for all his natur-philosophische outlook, was a skilled prac-tical chemist, who reported a good number of new preparations.He taught that matter was indestructible, illustrating this beliefbythe recovery of the original weight of a metal from the compoundsin which it was apparently disguised.

1 It is said that he made muchuse of the balance: his famous tree-experiment shows how deceptive

quantitative methods may be when applied within an inadequate

conceptual scheme. A younger iatrochemist (who also pursuedthe philosopher's stone) was Johann Rudolph Glauber (1604-70).He described for the first time the preparation of spirit of

salt (HC1), sodium sulphate, and perhaps chlorine. Glauber had a

sound insight into certain types ofchemical reaction, such as double

decomposition; for example, he explained the formation of"butter

of antimony" with sublimation of cinnabar from stibnite heated

with corrosive sublimate by saying that the spirit in the latter,

leaving the mercury, preferred to attach itself to the antimony in

the stibnite; the mercury then united with the sulphur in the

stibnite to form cinnabar.* From this example it is also clear that

Glauber employed the concept ofchemical affinity he understood

that one unit in a reaction might attract another more than a

third.

1 *

Since nothing is made from nothing, the weight [of one body] is madeof the equal weight of another body, in which there is a transmutation of

matter, as well as of the whole essence* (Prog. Afekori, 18). Van Helmont's

argument seems to be, that the same weight of prima maieria (water) is repre-sented by equal weights of any substance, irrespective of their densities.

1i.e., Sb2S8 + 3H.C1, = 2SbCls -f 3HgS. Double decomposition in this

same reaction was indicated rather less clearly by Beguin in the 1615 edition

of his Tyrocinium Chymicum. Cf. T. S. Patterson in Annals of Science, vol. II

(London, 1937), p. 278.


In 1675 tnere was printed for the first time a new textbook on

chemistry by a practical man, Nicholas Lemery (1645-1715),which remained popular for upwards of half a century. The title

of the Cours de Chymie contenant la maniere de fain les operations qui

sont en usage dans la Medicine sufficiently indicates its purpose. It

was a straightforward recipe-book, dealing first with the metals,

then with salts, sulphur and other minerals, and finally with

preparations obtained from vegetables and animals. Lemery was

not given to theorization, but he taught that there were, in addi-

tion to the three active principles mercury (spirit), sulphur (oil)

and salt, two passive principles, water and earth. He also acceptedthe theory due to Otto Tachenius that salt = acid -j- alkali, and

occasionally followed the particulate ideas of Descartes. The Cours

de Chymie was the most successful of many similar practical books

published at about the same time: an English example is GeorgeWilson's Compleat Course of Chymistry (? London, 1699). By the end

of the seventeenth century the best accounts of experimental

chemistry were those written with medical applications in mind,and though the old, esoteric iatrochemistry deriving from Para-

celsus had perished, future progress was to owe much to physiciansand apothecaries, among them Boerhaave, Cullen, Scheele andBlack. It is of significance also that the teaching of chemistry in

universities, beginning c. 1 700, everywhere placed it as an auxili-

ary to medicine. Even at the close of the eighteenth century most

of Black's pupils at Edinburgh were medical students. 1 From the

time of Boyle to that of Priestley and Cavendish the role of the

"amateurs" in chemistry was relatively insignificant, and the

reason is not far to seek. This was a period of rapid practical

development in the subject, but of minor theoretical expansion.It is therefore appropriate now to turn to this last of the great

philosophical chemists, Robert Boyle, who is one of the most

enigmatic figures of the scientific revolution. There can be nodoubt that he was one of its leading personalities, nor that he madewide, and incisive, use of the new ideas maturing in his time.

Whether he was himself capable of any major creative act in

scientific thought is more arguable. Possibly his originality (butnot his perseverance) as an experimenter has also been exagger-

ated; it is difficult to estimate accurately, since Boyle's works are

1 Cf. the interesting paper by Dr. James Kendall in Proc. Roy. Soc. Edin.,Section A, vol. LXIII (Edinburgh, 1952), p. 346 et seq.


perhaps the first to be filled with descriptions of experimentalresearch. These books, on which his fame was established, are

hugely prolix and sometimes tedious, containing masses of ob-

servations haphazardly selected and arranged, through which the

reader has to pick his way in search of the point of the discussion,

often to find that Boyle has been unable to make up his own mind.

Yet they are always redeemed by the sense of a sharp and con-

tinuous purpose, a far-reaching breadth of learning, and a humilityin face of the facts of nature that forbade dogmatism.The task Boyle set himself was to examine philosophically the

natural phenomena made known by chemical art; to determine

the underlying nature of the material transformations of whicha cumulative description had been built up since the time of

Libavius, and of the processes by which they were brought about.

He undertook to prove to philosophers that chemistry could be

more than a collection of recipes, and to the "chymists" that in

revealing nature's secrets they would have a more noble aim than

the concoction of medicines. Not that Boyle despised the applica-tion of chemistry to medicine. He regularly dosed himself and his

friends, and welcomed any new compound that promised thera-

peutic value, but he was aware that science as a whole is greaterthan the cure of disease. Boyle wrote no textbook of chemistry,like Lemery's, rather he usually assumed such a level of knowledgein his readers; nor was he greatly interested in the piling up of

more and more empirical knowledge for its own sake. Almost

always he wrote with a definite problem in mind, some aspect of

his ambition to restore natural philosophy as a unified whole, in

which chemical knowledge should play its due part. He sought to

build a bridge between chemistry and physics, the two sciences

concerned with the properties of matter, which ought to start

from common ground and be explicable one in terms of the other.

In this respect Boyle had much in common with van Helmont,whom he greatly admired (while admitting his frequent inability

to comprehend him); but whereas van Helmont had criticized

natural philosophers for their ignorance of ideas to which he him-

self had been brought by his own quasi-Paracelsian development,

Boyle proceeded quite differently. Essentially a physicist lookingat chemistry, Boyle sought to demonstrate that the facts and pro-cesses of chemistry were explicable in terms of the corpuscularian,mechanical hypothesis of matter which he had adopted.


In the first of his major works to be printed, which is also the

most widely read, this is certainly not very clear. The purpose of

the Sceptical Chymist (1661), as its title suggests, is negative, not

positive. It was to clear the ground of the three theoretical atti-

tudes to chemistry which were then in vogue. Boyle disposed

rapidly of the four Aristotelean elements, for they were no longer

plausible entities (at least to the progressive experimental

scientist).1 His main attack was upon the three principles of the

orthodox chemists, his real target. In this connection there was

nothing novel in his own definition of a chemical element, nor in

his insistence on the importance of discovering what the ultimate

constituents ofcompound bodies are. 2 He argued that none of the

chemists' principles could be extracted from metals like gold or

mercury; that their criterion of analysis by fire was in any case

faulty, since it could not divide glass into its known constituents,

sand and alkali. He pointed out (like van Helmont) that the

natures of bodies are not changed by entering into combinations,since the same bodies could sometimes be recovered separatelyin their original state. He emphasized acutely the illogicalities

and contradictions in which the ideas commonly entertained bychemists were involved. This criticism was warrantable, but in the

Sceptical Chymist Boyle equally proved that he could create nothingto take the place of that which he would destroy. No more than

any other contemporary did he believe that ordinary substances

gold, mercury, sulphur were elements, though they resisted

analysis. He used van Helmont's tree-experiment (which he re-

peated) to show that vegetable matter could be formed from water

alone, without the participation of earth and fire, or salt and

sulphur, but he did not believe that all things were made of watej.

In the end Boyle failed not only to draw up his own list ofchemical

elements, but even to decide definitely whether such simplesubstances do exist at all.

1 However, they were by no means dead. The four Aristotelean elementswere still to recur in the eighteenth century, whether in Chambers'* Dictionaryor in P. J. Macquer's Dictionnaire de Chymie, where it is said (s.v. l4mens)'on doit regarder en chymie le feu, Pair, 1'eau et la terre, comme des corpssimples.'

2 Cf. The definition ofvan Helmont (Prog. Meteori, 7):* An element would

cease to be a simple body, if it were divisible into anything prior, or moresimple. But nothing among corporeal things is granted to be prior to, or moresimple than, an element.' Boyle did not claim any originality for himself,rather admitting that his definition was a common one.


There was, indeed, sufficient reason in his corpuscular physics

why he should have been doubtful, why he should have thoughtthat anything might be transmuted into anything else, by nature

if not by art. 1 Some of the evidence is set forth in the Sceptical

Ghymist: Boyle believed, with most of his generation, that metals

and minerals like saltpetre "grew" in the earth. These substances

were not themselves elements; neither were they formed from

pre-existing elements, for such elements could not be traced in the

earth where the growth occurred. 'From thence' wrote Boyle'we may deduce that earth, by a metalline plastick principlelatent in it ["seed"], may be in process of time changed into a

metal' a common enough opinion.2 From a survey of pheno-

mena of this kind he came to the conclusion that transmutations

in the chemical sense were possible by means of this "plastic

power" in the earth, as also by the "seminal virtue" in seeds (for

the salts etc. in wood were certainly not present as such in the

water with which the tree was nourished). However puzzling this

might be from the chemist's point of view, it was not at all inex-

plicable to the physicist in Boyle, for his physical theory of matter

taught him that all substances are made up of the same funda-

mental particles.3

Since, therefore, substances differ from one

another only in the 'various textures resulting from the bigness,

shape, motion and contrivance of their small parts, it will not be

irrational to conceive that one and the same parcel of the universal

matter may, by various alterations and contextures, be broughtto deserve the name, sometimes of a sulphureous, and sometimes

of a terrene or aqueous body.'4

The theory of matter which Boyle favoured led him to believe

(as he acknowledged in the early pages of the Sceptical Chymist]

that in its basic and primitive form matter existed as 'little

1 One transformation in which Boyle was naturally very interested was that

of base metals into gold. Like Newton he seems never to have been altogetherconfident that this transmutation, though theoretically attainable, was actually

practicable.1 Works (London, 1772), vol. I, p. 564. Boyle cited Cesalpino and Agricola

for the statement that metals reappear in previously worked-out veins. For

Agricola's belief that metals are generated from the Aristotelean elements

earth and water, cf. De re metallica (New York, 1950), p. 51, note.8 A modern analogy would be the proposition that the chemical element is

an unsound and illogical concept, since all are composed of the same sub-atomic

particles.4 Works (London, 1772), vol. I, p. 494,


particles, of several sizes and shapes, variously moved.' These

were further organized into 'minute masses or clusters/ beingthe 'primary concretions' of matter, some of which were in

practice indivisible. Hence the clusters that compose gold, beinginviolable by the ordinary chemist's art, could always be recovered

from any compound of the metal. But a mass of such corpuscleswas not an element, for as Boyle stated, the particles of two sets of

corpuscles might so regroup themselves that 'from the coalition

there may emerge a new body, as really one, as either of the

corpuscles was before they were mingled.'1 Thus vinegar acting

upon lead formed the "sugar" of lead (lead acetate) but by no

means could the acid spirit of vinegar be recovered from the new

compound; Boyle thought its corpuscles were destroyed. Theindivisible corpuscles of glass were formed by a "coalition" of

those of sand and ashes; so that resistance to chemical analysis byfire or acids was not a test ofelementariness: for such indestructible

corpuscles could as well be found in the bodies due to art, as in

those due to nature. The same experience that taught Boyle that

glass was not to be numbered among the elements, prevented himfrom knowing whether gold was one or not: he thought it was

probably not.

It is plain that Boyle's corpuscularian philosophy, in many waysso fertile, prevented him from taking any step towards the modern

conception of the chemical element (an achievement usuallycredited to him). In fact it led in the opposite direction, for so

long as Boyle, the physical chemist, concentrated on explanationsofchemical reactions in terms ofcorpuscles and particles, he wouldbe the less likely to believe that if elements existed at all, their

existence was very significant to his new outlook. Lavoisier deter-

mined that if a body resisted chemical analysis it should be

accepted, pragmatically, as an element. Boyle could not havedone this, because he thought in corpuscular terms. No body made

up of corpuscles could be simple, homogeneous or elementary in

the strict sense, because the corpuscles themselves were com-

pounded of a variety of particles. The pragmatic test of resistance

to analysis proved only that some concretions of these particlesinto corpuscles were more coherent than others, whether broughtabout by nature (gold) or by art (glass). But coherence andelementariness could not be equivalent, since Boyle knew that

1 Works (London, 1772), vol. I, pp. 474-5, 506-7.


some corpuscles whose coherence resisted analysis were factitious,

i.e. non-elementary.The impasse was complete, and Boyle could not avoid it. Nor

was it really important for him to do so: the truth that chemical

changes occur by modifications of corpuscular structure, and byre-shuffling of the particles within corpuscles, was far more sig-

nificant to him than a dubious search for primary elements, whoseexistence he was quite content to regard as hypothetical. In this

he may be said to have anticipated the attitude of a modern

physical chemist who (of course within a far more rich and

exact conceptual framework) thinks in terms of molecules, atoms,ions and kinetic theory, without paying much attention to the

elementariness of hydrogen or carbon.

That Boyle's chemical theory was predominantly shaped by his

corpuscularian physics is apparent from many works beside the

Sceptical Chymist. He was no dogmatist, he was no follower of

systems, he believed that hypotheses should be framed to fit the

facts, but it was quite clear to him that complete scepticism and

abhorrence of all theory were antithetical to true philosophy.1

Indeed, his ambition to bring chemistry into natural philosophywould have been meaningless had he not had a theory of natural

philosophy, essentially a theory of matter, to hand for the purpose:

I hoped I might at least do no unseasonable piece of service to the

corpuscular philosophers, by illustrating some of their notions with

sensible experiments, and manifesting, that the things by me treated

of may be at least plausibly explicated without having recourse to

inexplicable forms, real qualities, the four peripatetick elements, or

so much as the three chymical principles.2

Thus for Boyle solution always represented the interspersion of

the corpuscles of the solvent among those of the dissolved body,heat consisted of material particles, and "air" of all kinds mainlyof elastic corpuscles of a particular type, among which the

mingling of other corpuscles gave each "air" its own character.

He constantly attributed the properties of acids, oils, salts, etc.

to the nature of their component corpuscles. In fact the theory was

brought into play whenever Boyle commented on a chemical

experiment. Instances are particularly numerous in the Origin of

Forms and Qualities, where (as examples chosen at random) he

1 Gf. Ibid., p. 591.2 Certain Physiological Essays (1661), Works

',vol. I, p. 356.


spoke of 'the body of silver, by the convenient interposition of

some saline particles [being] reduced into crystalsJ

of Luna cornea

(silver chloride) ; or, of another experiment,'

considered that the

nitrous corpuscles [of nitric acid], lodging themselves in the little

spaces deserted by the saline corpuscles of the sea-salt, that passedover into the receiver, had afforded this alkali';

1 or again declared

that

the more noble corpuscles which qualify gold to look yellow, [andto resist nitric acid] . . . may either have their texture destroyed

by a very piercing menstruum, or, by a greater congruity with its

corpuscles, than [with] those of the remaining part of the gold, maystick closer to the former and ... be extricated. 2

Corpuscularian ideas were especially developed by Englishscientists in relation to the allied reactions of combustion andcalcination. Both were anciently regarded as separations: the

ash or calx (oxide) remaining was an earthy residue left after the

more volatile parts of the combustible or metal had been driven

off by fire. It was well known, however, that the calx (oxide)

exceeded the original metal in weight: whence Jean Rey was led

to believe (in 1630) that though the calx was lighter than the

metal in nature, it became heavier by the attachment to it of air

which had become thickened in the furnace. Boyle later thoughtthat the increased weight came from fire-particles penetratingthe walls of the crucible and impregnating the calx. This explana-tion was widely accepted until it was decisively confuted byLavoisier. With regard to combustion it was well known to Boyleand others that bodies would not burn without air, unless (like

gunpowder) they contained some nitrous material. A familiar

experiment (originally described by van Helmont) showed that

when a candle was burnt in a closed vessel over water, the air

within diminished and the water rose up inside. From these andother observations Robert Hooke sketched a theory in Micrographia

according to which combustible bodies were dissolved by a certain

substance present in the atmosphere, this solution (like others)

evolving great heat, and thus flames, which Hooke took to be

'nothing else but a mixture of Air, and volatil sulphureous partsof dissoluble or combustible bodies, which are acting upon each

1i.e., KC1 + HNO8

= KNO3 + HC1.1

Origin of Forms and Qualities, Section VII. Boyle is obviously far from

thinking that gold might consist of a single kind of corpuscle.


other.' This aerial substance he identified with 'that which is

fixt in Salt-peter* This same theory was elaborated in much greaterdetail by the physician John Mayow in 1674, who also set it

uncompromisingly in the corpuscularian framework. In his view

the atmosphere consisted of a mass of air-corpuscles with whichwere mingled others that he called

"nitro-aerial particles,"

because they were fixed in nitre and nitric acid. These nitro-aerial

particles were highly elastic, and responsible for the hardness of

quenched steel. They also corroded metals exposed to the air.

The same particles, reacting violently with the sulphureous

corpuscles of combustible bodies, produced heat and flame, as

Hooke had said; therefore combustion could not occur without

them. Air in which combustion had taken place was (in some

way which Mayow did not explain) deprived of its nitro-aerial

particles, thereby decreasing in elasticity and causing the water

to rise in van Helmont's experiment. Similarly air breathed byanimals lost its nitro-aerial particles, so that the expired air wasless elastic (i.e. occupied a smaller volume) than that inspired;the same particles caused the blood to ferment and provokedanimal-heat. They caused fermentation generally; they formed

the fiery body of the sun, and the flash of lightning; in short, the

nitro-aerial particle became in the hands of Mayow a deus ex

machina for explaining many totally unrelated phenomena. Hehad no idea that these particles made an "air," or that the

atmosphere was a mixture of "airs" of which that was one. Thenotion (first put about by Thomas Beddoes, Davy's patron) that

Mayow had closely anticipated the oxygen-theory of Lavoisier

cannot support serious examination: his was c. typical corpuscul-arian philosophy.

During the next hundred years studies on combustion andcalcination were to prove vital to the progress of chemical theory,while the accumulation of empirical fact was proceeding in a waywhich rendered the dubiety of theory almost irrelevant. The

attempt to explain chemical reactions in terms of the mechanistic

theory of matter, begun by Descartes and continued by Boyle,

Mayow and others, was abandoned in the early years of the

eighteenth century. Its claims were too wide, its achievements too

lacking in definition. Not that chemists doubted the particulatestructure of matter, but since nothing was known about the size,

hardness, shape, etc. of corpuscles, statements in which these


properties of the fundamental constituents ofmatter were involved

were recognized as meaningless. This downfall of Boyle's hopesthe cause of the subsequent neglect of the theoretical import in

his writings was accelerated by the ascendancy of Newtonian

mechanics. The laws which governed the stars must be applicablealso to the smallest particles of matter, and the laws of chemical

affinity be subject to the supreme law of gravitational attraction.

The elements of this theory, already sketched by Newton in the

Queries to his Opticks (1704),* were soon after worked out more

completely by Keill and Freind. The later empirical study of

affinity (e.g. by Geoffroy, who published tables of affinity in 1718)was certainly encouraged thereby, but after the middle of the

century (when attraction had long been abandoned by practical

chemists) it became clear that the property of attraction in

corpuscles was as intangible as their other properties: nothingcould be said about it, other than that it existed. And so the am-bition to render chemistry a branch of physics was, for the time,

frustrated. Dalton's atomic theory was conceived entirely in a

chemical context, and it was under the aegis of chemistry that the

second penetration of atomism into modern scientific thought was

to take place.

If to many chemists of the early eighteenth century it seemed

hopeless to base their theories directly on the properties of atoms

or corpuscles, they were not the less convinced of the existence of

elements or principles of an ultimately corpuscular nature. The

principles adopted by the German chemist G. E. Stahl (1660-

1734) from the writings of J. J. Becher (whose Physics Subtenant

of 1669 Stahl republished in 1703) were accepted by most of his

colleagues, especially those in Germany and England, until near

the close of the century. Stahl's principles were water and three

kinds of earth: air was not chemically active. The three earths

corresponded to the three principles of the iatrochemists, but

Stahl preferred to call the second (sulphur) phlogiston. Thefollowers of Stahl made much use of affinity in explaining reactions

(meaning, in this case, the tendency of like to react with like)2

1 Newton's investigations into chemistry were almost completely unknownin detail at this time, as indeed they still are.

* Thus Junker on the formation of corrosive sublimate (Helene Metzger,Newton, Stahl, Boerhaave et la Doctrine Chimique (Paris, 1930), p. 142):

*Commonsalt consists ofan acid and an alkaline base. Vitriolic acid, being more powerful,seizes the base and drives out the acid from the salt. This acid would escape


and of a novel theory of salts (as earth + water) . The theory of

phlogiston was far from being the whole of their chemical doctrine,

though it was the dominant feature of that doctrine because it

permitted the co-ordination of many previously isolated facts. 1

Phlogiston was the substance emitted during combustion and the

calcination of metals, the "food of fire" or" inflammable prin-

ciple." The complete, or almost complete, combustion ofcharcoal,

sulphur, phosphorus, etc. demonstrated that these bodies were

very rich in phlogiston: while the formation of sulphuric acid,

phosphoric acid, etc. from the solution of the fumes produced bycombustion demonstrated that the substances themselves actuallyconsisted of nothing but the acid joined to phlogiston ('.e. sulphurminus phlogiston > sulphuric acid : therefore sulphuric acid +phlogiston = sulphur). When a metal was heated, the phlogistondriven off left a calx behind (therefore calx + phlogiston= metal).

Conversely, by heating the calx with charcoal, phlogiston was

exchanged and the metal restored. Many reactions became

comprehensible when interpreted in terms of an exchange of

phlogiston, so that often where a modern chemist sees a gain or

loss of oxygen, Stahl saw an inverse loss or gain of phlogiston.

Oxygen has weight: and a modern chemist would insist that

phlogiston ought to have negative weight, a suggestion actuallymooted when Stahlian chemistry was already moribund. Thematter was not serious at first. Boyle himself had explained the

increased weight of a calx in a way that nowhere conflicted with

the idea of phlogiston. Until such time as gases were collected,

and the gain or loss of weight due to the participation of a gaseouselement in a reaction could be correctly estimated by means of

the balance, it was impossible to achieve a balance of masses in a

chemical equation. Chemical mathematics, before 1775, was such

that there was no palpable absurdity in the conception of

phlogiston as a material fluid: as Watson said,

You do not surely expect that chemistry should be able to present youwith a handful of phlogiston, separated from an inflammable body;

you may just as reasonably demand a handful of magnetism, gravity,

freely, but meeting with another substance (mercury) with which it has some

analogy (though not so great as with its own base), it forms a saline substancewith it. This substance (corrosive sublimate) is volatile because both mercuryand the acid from salt are volatile: they have an identity of "mercurial

principle".'1 This is particularly emphasized by Mme. Mctzgcr, op. cit.

328 THE SCIENTIFIC; KEVULUTIUIN

or electricity. . . . There are powers in nature which cannot otherwise

become the objects of sense, than by the effects they produce; and of

this kind is phlogiston.1

The purely logical objection which has often been raised against

the phlogiston theory is therefore of small value. Eighteenth-

century scientists readily admitted the existence of weightless,

impalpable fluids such as electricity and caloric. Caloric was

indeed phlogiston revived, stripped of its chemical attributes to

become Lavoisier's "pure matter of heat." 2 Nor did StahFs

influence check the progress of chemistry as an empirical science;

rather his views provided a useful provisional scheme for the

explanation ofmany experiments. As such many chemists accepted

them, without sacrificing their liberty to interpret experiments in

the light of the evidence alone. Lavoisier himself was at first far

more keenly aware of the need to scrutinize experimental data,

than of any implausibility inherent in the phlogistic doctrine

itself. The practical chemists were always far more interested in

particular problems than in universal theories; some, like Boer-

haave, were never followers of Stahl. Hence it seems unnecessaryto suppose that the fortunes of chemistry were inextricably bound

up with those of the phlogiston theory, whose scope was largelyrestricted to the phenomena of combustion and calcination; but

it is certain that the age of phlogiston witnessed great progress in

chemical experimentation, though the hypothesis has so often been

characterized as futile and retrogressive. In the phlogiston periodthe chemistry of gases was begun by Black, Cavendish, Scheele

and Priestley; the vain attempt to base chemical theories on

organic and inorganic reactions conjointly was abandoned; there

were striking improvements in the analysis of inorganic com-

pounds. Considerable development in the application of chemistryto manufacture also took place. By contrast, few comparablediscoveries can be linked with the corpuscular chemistry of Boyleand Mayow.

Irrespective of its ultimate redundancy, phlogiston was un-

doubtedly a useful concept until about 1 765, when the systematic

1 Richard Watson: Chemical Essays, vol. I (London, 1782), p. 167.* Compare Watson on phlogiston:

*

Chemists are of opinion that fire enters

into the composition of all vegetables and animals, and most minerals; andin that condensed, compacted, fixed state, it has been denominated the

phlogiston.* (Op. a/., p. 165.)


study of gases was begun by Henry Cavendish (1731-1810). It

enabled a consistent interpretation to be given to experiments on

combustion, and many others involving oxidation and reduction. l

Chemists gained a valuable insight into a number of reactions in

phlogistic terms, and so learnt to treat natural substances

sulphur, carbon, salts, alkalis, acids, metals, earths, and so forth

as the really active participants in their processes. Lavoisier's

chemical revolution was based on a level of factual knowledge,and a pragmatism with regard to chemical combination, un-

equalled at any earlier time. The fact that it often happened that

Lavoisier could simply invert the phlogistic doctrine is evidence

of the service which the phlogistonists had performed. Only with

the discovery of the common gases when hydrogen was taken to

be pure phlogiston, nitrogen to be phlogisticated air, oxygen to

be dephlogisticated air, etc. did phlogiston become a serious

impediment to the interpretation of experimental work; only then

did the question of its usefulness as a hypothesis become really

significant.

The technique of collecting gases over water was invented by

Stephen Hales before 1720; Joseph Priestley (1733-1804) substi-

tuted mercury when working on water-soluble gases. Hales

examined "airs" produced in a variety of chemical processes,

particularly in order to discover the quantity evolved from a given

weight of materials, but he drew no new qualitative distinctions

between them. From his experiments he concluded that "air"

was capable of being fixed in substances as a solid. The first

chemist to label such a "fixed air" decisively, at the same time

discovering its function in a number of reactions, was Joseph Black

(1728-99). The linkage is important, for many "airs" had been

1 It is not difficult to find examples of reasoning in phlogistic terms whichled to satisfactory experimental procedures. Thus Scheclc (1779) wished to

establish the ratio by volume of "pure air'* (oxygen) to "foul air'* (nitrogen)in the atmosphere. He argued: 'When this pure air meets phlogiston uncom-bined, it unites with it, leaves the foul air, and disappears, if I may say so,

before our eyes. If, therefore, a given quantity of atmospheric air be includedin a vessel, and meet there with some loosely adhering phlogiston, it will at

once appear, from the quantity of foul air remaining, how much pure air wascontained in it before.' He therefore took a small amount of iron filings, mixedwith sulphur and a little water, which he knew to be a preparation very rich

in phlogiston, and used it to effect the "disappearance" of the "pure air" in

a known volume ofcommon air. Scheele's mixture does in fact take up oxygenvery readily. The result he obtained (9 : 24) was not good, but his procedurewas perfectly correct. (Cf. Chemical Essays (London, 1901), pp. 190-4.)


roughly identified in the past (e.g. as inflammable, or extinguish-

ing flame), but none had been clearly described as being distinct

in species from common air, nor had any function been ascribed

to them as participants in chemical processes. The most striking

part of Black's work (Experiments upon Magnesia albay etc., 1756)was his proof that quicklime was lime deprived of "fixed air": the

quantitative relation was completely established. Black found that

a mild alkali became caustic through loss of its"fixed air," and

that "fixed air" was emitted with effervescence when lime was

dissolved in acids. He made constant use of the concept of affinity

in explaining his experiments: thus, discovering that when quick-lime was added to a mild alkali, the original weight of lime 1 was

precipitated and the alkali rendered caustic, he said that "fixed

air" had been exchanged because of its greater affinity for quick-lime than for the alkali. He carefully pointed out that thoughboth water and the atmosphere contained "fixed air," it was not

identical with "common air." Later he discovered it in exhaled

breath, and in common air passed over burning charcoal: the

precipitation of lime from lime-water proved to be a specific test.

The whole essay was a neat model of scientific method: at one

stage in his work Black drew up a list of predictions, each ofwhichhe was able to verify by experiment, thus proving that "fixed air"

played the part he had assigned to it.

In all this there was no mention of phlogiston. Though Black

was very far from rejecting the phlogiston theory in its entirety

until long after this time, he was convinced that his experi-ments could be explained without phlogiston, and he resisted all

attempts to argue that phlogiston was involved in them. Black

had not, in 1756, actually collected his "fixed air," for the tech-

nique of imprisoning fugitive "elastic fluids" in vessels was still

almost unknown to chemists. It was described by Cavendish in

his paper On factitious airs (1766), and thereafter widely used. Hedistinguished between Black's "fixed air" and another (hydrogen)

deriving (as he thought) from metals, which he found to be lighter

than common air. At about the same time the Swedish apothecaryCarl Wilhelm Scheele (1742-86) separated the two major con-

stituents of the atmosphere "Feuerluft" (oxygen) and "verdor-

bene Luft" (nitrogen): he also prepared oxygen in various waysin the laboratory, as did Joseph Priestley, quite independently, in

1 Calcined by Black to make the quicklime.


1774. Most of the characteristic qualities of these and other gaseswere noted.

Such were the strategic few, among a great number of other

major discoveries made by chemists who thought without reserva-

tions in the framework of which phlogiston was an essential part.

Two of the pioneers of gas chemistry, Priestley and Cavendish,were never reconciled to Lavoisier's doctrines. Their refusal wasno doubt due to rigidity of mind, but it points also to the fact that

the phlogistic theory had imposed no barrier upon the activities

of these skilful experimenters. It also emphasizes Lavoisier's own

originality in devising new interpretations of their experiments.While the adherents of phlogiston were by no means agreed in

the details of their exposition Priestley, for example, thinkingof oxygen as dephlogisticated air, and Cavendish preferring to

treat the gas as dephlogisticated water a situation by no meansunusual on the frontier of research, these hesitations did not

inhibit inquiry; on the contrary, it is quite clear that Scheele,

Priestley and Cavendish were each at times induced to makecertain fertile experiments by reasoning in the phlogistic manner.

The situation in which the further progress of a branch of

science is directly dependent upon an adequate matching of

theoretical concepts and experimental facts is by no meansuncommon. This was certainly the case when Galileo and Newton,

respectively, revised the concepts of mechanics, and again with

physics in the nineteenth century. But though such a matching of

fact and theory is always useful it is far from being invariablyessential. Did such a situation exist in chemistry at the end of the

eighteenth century? The evidence would seem to suggest that it

did not. The empirical attitude of the great experimenters was in

reality far more important than their theorization: it is therefore

the less likely that any plausible modification of the doctrines

prevailing through the first three-quarters of the eighteenth

century would have had much influence on the course of events.

No one would deny that Lavoisier was the first chemical theorist

of genius. No one would deny that his interpretation of the

phenomena was far superior to that of the phlogiston theory: it

was one upon which the ultimate advancement of chemical

knowledge depended. Yet it is also perfectly clear that the

inventive empiricism of his contemporaries was just as necessaryfor this as his own logical, interpretative intellect, and that,


moreover, the rapid progress of chemistry in the nineteenth

century owed a great deal to developments, such as electro-

chemistry and the atomic theory, to both ofwhich Lavoisier's own

insight into the nature of chemical reactions contributed nothing.Antoine Laurent Lavoisier (1743-94) was, like Newton, less

the author of new experiments than the first to realize their full

significance. Experimentation for its own sake, which delighted

Priestley, had little appeal for him. In his laboratory work he

proved himself a skilful analyst, and an able exponent of the

quantitative methods of Black and Cavendish, but not greatly

imaginative in the way that Cavendish (or, later, Faraday) was a

supremely imaginative experimenter. None of his most famous

experiments was new: the element of originality in them was

limited to Lavoisier's insistence upon paying heed to the teachingsof the balance:

We may lay it down as an incontestable axiom, that, in all the opera-tions of art and nature, nothing is created; an equal quantity of

matter exists both before and after the experiment; the quality and

quantity of the elements remain precisely the same; and nothingtakes place beyond changes and modifications in the combination of

these elements. 1

His first investigation was into the composition of the water in

various localities about Paris. In his second he refuted the ancient

fallacy that water was converted into earth by long heating and

evaporation: he found that the "earth" obtained was dissolved

glass. Thirdly, he discovered that air was "fixed" in phosphorus

pentoxide and sulphur dioxide (made by burning phosphorus and

sulphur), bringing about an increase of weight. He predicted that

the same would be found true of all combustibles, and that the

increased weight of metallic calces was due to a similar fixation of

air. This last prediction he confirmed (1772), by reducing lead

oxide to lead with charcoal: a large quantity of air was evolved.

Lavoisier had set out to produce facts, and by quantitativemethods he had succeeded. Some of them were not exactly new,

though they had formerly been less precisely stated, but he per-ceived that there was enough to make the phenomena ofcombustion

1 Elements of Chemistry (trans, by Robert Kcrr), (Edinburgh, 1790), p. 130.But Lavoisier was in no sense the first chemist to subject notions of chemical

composition to quantitative tests. There are many earlier examples of this

procedure.


and calcination worthy of detailed examination. All his future

success followed from his apprehension of this significance. Heembarked upon 'an immense series of experiments' intended to

reveal the properties of the different "airs" involved in chemical

reactions, which seemed '

destined to bring about a revolution in

physics and chemistry.' In fact, however, Lavoisier's qualitative

study of gases did not advance very far between February 1773

(when he wrote the note just quoted) and October 1774, thoughhe did satisfy himself that the "air" given off in the reduction of

lead oxide with charcoal was Black's fixed air, and that Boyle's

explanation of the origin of the increased weight of metallic calces

was false.1 At this stage he was still uncertain whether the "air"

combining with metals to form their calces was Black's fixed air,

or common air, or something occurring in the atmosphere. Hehad, apparently, missed the importance of Black's own observa-

tion that burning charcoal was a source of his fixed air. He could

hardly have claimed, at this point, to have done more than

indicate a series of reactions in which some kind of air was

involved, parallel to those already described, more completely,

by Black.

In October 1774 Lavoisier was informed by Priestley himself of

the evolution of an "air" (oxygen) from the red calx of mercury(mercuric oxide) when reduced by itself to the metal with the aid

of a strong heat. 2 Some months later Priestley had established that

this "dephlogisticated air" (as he now called it) was respirable as

well as capable of supporting combustion. Soon after Lavoisier

was able to report new experiments to the Academic des Sciences:

the calx of mercury reduced with charcoal gave fixed air, reduced

alone it gave off Priestley's new air. Therefore it was, said

Lavoisier, common air in a highly active state which combinedwith metals to form their calces. Evidently he did not yet regardit as a particular constituent of the atmosphere, a view which he

adopted in the course of the next two years, when he realized that

one fraction of the air was inert during combustion and calcina-

tion. This he called mofette. The atmosphere, therefore, contained

two "elastic fluids," as Scheele had discovered some time before.

1 In this he had been anticipated by the Italian chemist, Beccaria. Theequivalence of the increased weight of the calx with the weight of the air

admitted when the retort was opened was not as exact as Lavoisier wished.1 Lavoisier's own claim to the discovery of oxygen is generally rejected.


By August 1778 Lavoisier could announce that "eminently

respirable air" (the"dephlogisticated air" of Priestley) combin-

ing with a metal, formed a calx, and that the same air combiningwith charcoal gave Black's fixed air (carbon dioxide). The prob-lem of calcination was thus solved, and other discoveries followed

rapidly. Lavoisier found that sulphur and phosphorus, in burning,also combined with "eminently respirable air" only, and that it

was this combination that yielded acids by solution in water. Hefound the same air in nitric acid, and was led to conclude that it

was present in all acids. In respiration, the mofette part was exhaled

unchanged, but the respirable part was exhaled as the fixed air

which Black had found in the breath. From experiments carried

out in collaboration between 1 782 and 1 784 Laplace and Lavoisier

judged that respiration was a process- of slow combustion, for the

amount of heat produced by an animal in breathing out a certain

volume of fixed air, was almost equal to the amount produced in

burning enough charcoal to give the same volume.

In his memoirs before 1778 Lavoisier had not eschewed the

word "phlogiston" completely, though he was uncertain of its

role in his experiments, if it existed at all. By 1778 the elements of

his new theory of oxidation were quite firm, and in it phlogistonhad no part for he had proved that the phlogiston-concept was

the inverse of the truth. The processes of oxidation (combustion,

calcination) were not analyses but syntheses, in which phlogistonwas as redundant as it was in Black's fixed-air reactions. Oncethe pattern of the substitution of the oxygen-concept for the

phlogiston-concept became clear, it could be extended to whole

groups of reactions, over almost the whole area of chemistry, bythe development of suitable analogies. Indeed it was possible to be

deceived by such analogies.1Proceeding in this way, it became

ever more plausible to propose the exclusion of phlogiston from

1e.g. in Lavoisier's account of the relation of "oxygenated muriatic acid"

(chlorine) to "muriatic acid" (hydrochloric). Lavoisier was convinced that

the latter was a compound of an unknown base with oxygen (as were all acids,in his view), and the former a compound of the same base with a higherproportion of oxygen (by analogy with sulphurous, sulphuric acids, etc.).

Therefore he postulated 2XO -f . . . O, -* aXO2 + . . . for 4.HC1 + . . . O,-> Cla + aH2O 4- His name for it was simply the inverse of "dephlogisti-cated marine acid gas" (Scheele) and really considerably less appropriate,since if hydrogen = phlogiston (Cavendish), KG1 H -> Gl. (Cf. Elements ofChemistry, pp. 69-73, 233-5). Davy discovered the true composition of HG1,and established that chlorine is an element.


the doctrine of chemistry altogether. In 1783 Lavoisier was

impelled to make a direct attack upon the phlogiston theory,

which he seems to have disliked even before he had any very solid

grounds for doing so. In this comparison of his own theory with

that of the phlogistonists, he insisted upon their inconsistencies

and duplications of hypothesis much as Galileo had analysed the

weaknesses of his opponents long before. Phlogiston was not

merely superfluous; it had come to mean quite different things in

different contexts, and had become a mere drudge in chemical

theory.From this time the number of adherents to Lavoisier's views

increased steadily, first in France, and then abroad. One serious

difficulty remained. Lavoisier had not been able to discover the

product of burning "inflammable air" (hydrogen) with commonair, or with "respirable air" (oxygen). Nor could he account for

the evolution of hydrogen when metals were dissolved in weak

acids, and its non-appearance when the calces of metals were so

dissolved. All this could easily be explained in terms of phlogiston.Once again enlightenment came from the English experimenters.In 1 782 Cavendish continued experiments begun by Priestley andothers in which an electric spark was passed through mixtures of

hydrogen and common air. The work was done with wonderful

neatness, and he was able to identify the condensate inside his

glass vessel as common water, the gases disappearing in a ratio of

2:1 by volume. By June 1783 these experiments were known to

Lavoisier, who, paying Cavendish scant tribute, hastily repeatedthem. Initial scepticism was replaced by a rapid reinterpretationin terms of his theory: water was the oxide of hydrogen, and

hydrogen was evolved by the action of metals from the water

present in the weak acids.

The last act in the "chemical revolution" was the establish-

ment of a new terminology. The existing names of compoundswere either misleadingly descriptive ("butter of antimony"), or

redolent of the displaced theory ("dephlogisticated air") andeven older notions ("spirit of salt"), or based on common words

like "salt" and "earth." In 1787 Lavoisier and three of his

French adherents devised a new nomenclature, still substantially

preserved, in which the names were intended to identify the

nature of the substances. Thus hydrogen (water-former) replaced"inflammable air" and oxygen (acid-former) "eminently respirable


air." Mofette became azote (inert) or to non-French chemists

nitrogen (nitre-forming). Compounds of an element with oxygenwere all oxides, with sulphur sulphides ,

etc. This aim to establish

regular patterns of nomenclature has been consistently followed.

At the same time Lavoisier abandoned the attempt to seek (in

chemistry) any reality more fundamental than that revealed by

ordinary analysis. Substances which resisted analysis were, to him,

elements; for example the common gases, metals, sulphur, carbon,

lime, and a number of earths and other"radicals" some of which

were soon analysed into other constituent elements. Lavoisier

already used the word "radical" in the sense of a unit in chemical

reactions, and an element was simply an indestructible radical.

All this was fully explained in the first textbook of the new

chemistry, the Traitt JElementaire de Chimie of 1 789.

Its publication draws a convenient line of demarcation. Yet it

is important to recognize how little, as well as how much, was

really new in it. The theory, and the arrangement based upon the

theory ofchemical combination, was all Lavoisier's. The inorganic

experiments and substances described had almost all been knownfor twenty years, and the majority for much longer. Lavoisier andhis friends, however, had created the organic section (dealingwith the composition of alcohol and sugar, etc.) almost unaided.

If the table of elements was new, it derived (by a simple modifica-

tion) from the older chemists' practical habit of treating phos-

phorus, sulphur, metals, etc. as virtually compounds of element

-}- phlogiston. Lavoisier still spoke of earths and alkalis much as

they had done, and knew little more about them. On the mysteryofchemical affinity he said nothing, on the plea that it was unsatis-

factory to discuss it in an elementary treatise. Perhaps it is most

surprising, in the beginnings of modern chemistry, to discover

Light and Heat listed as elements. 'Light,' wrote Lavoisier,*

appears to have a great affinity with oxygen . . . and contributes

along with caloric to change it into the state of gas.' It also com-bined with the parts of vegetables to produce their green pigment.

1

Lavoisier also regarded light as a modified caloric, or vice versa;

this caloric, the invisible, weightless matter of heat was essential

to his view of matter. Caloric was interspersed between the

particles of bodies: in small measure in the solid, to a great extent

in the liquid, and most of all in the gaseous state when (so to

1 Elements of Chemistry (trans, by Robert Kerr), (Edinburgh, 1790), p. 183.


speak) the particles of matter floated freely in the fluid. Oxygengas was really oxygen matter plus caloric, which was liberated as

free heat when the oxygen became "fixed" in combination with

a combustible. Caloric also caused the physical expansion of

heated bodies, by pushing their particles farther apart. Here are

undoubted vestiges of corpuscular mechanism in Lavoisier's

thought, when he handled (in a method which would have been

familiar to Boyle, but unacceptable to him) the problem of the

origin of heat and flame, which had so much puzzled Boylehimself. Here, on the boundary of physics and chemistry, the

ideas of the seventeenth-century physico-chemical corpusculariansstill survived.

What Lavoisier did is clear enough: how was he able to do it?

Disregarding the noisy disputes of theorists and rival interpreta-tions of this or that experiment, factors can be discerned beneath

the surface, not always conspicuous to the great theorist himself,

leading towards the chemical revolution. Some are fairly obvious:

for example, increased reliance on quantitative procedures. Whatwas important here was not the mere tabulation of weights and

measures, still less the making of a serious mistake like Boyle's

(p. 324) for numerous exposures of the error failed to make plainits momentous importance but rather use of measure for con-

structive purposes, to arouse or to answer questions. "Let us

regard the facts without prejudice" said Lavoisier; but a table of

facts concerning quantitative reactions is not, and can never be, a

chemical theory. He might rather have said "Let us be astonished

when wo contrast the facts with the expectations created by our

theory." This was the spirit of Galileo's, of Newton's, of Black's

researches. Rigorous quantitative methods were only useful in

proportion as they brought about a sharper juxtaposition of fact

and theory, of the flint and steel to which Lavoisier supplied the

tinder.

In the second place, the work of the great theorist co-ordinated

that of the great experimenters in more senses than one. Theysupplied him with the pieces whose interlocking provided a perfect

picture, and they also built the framework of chemical knowledgewithin which alone his theory could carry conviction. If Lavoisier's

prime experiments were rarely of his own invention, they were

the more telling in that they were familiar, in the same way that

Galileo's reasoning was the more forceful because it was focussed


on commonplace experiences. As a third example, it may be

observed that Lavoisier extended to its logical conclusion a

practical, pragmatic way of thinking about the matter in a

chemist's retort which went back at least to the mid-seventeenth

century. Earlier chemists had thought of a salt as a metal-stuff

and an acid-stuff in combination, had carried out analyses in

terms of the sulphur-content, metal-content, alkali-content andso forth of the original material, and having come to see chemical

reactions as a process of subtraction and addition, they hadinvented the theory of affinity to account for it. To this chemist's

attitude to matter and its transformations ignoring the questionof the ultimate physical reality of what took place Lavoisier

brought rigour and precision, but it can hardly be said that he

created it. Perhaps in this was the core of the chemical revolution,

that it severed chemistry from physics, albeit temporarily. Boylehad been frustrated because he tried to explain chemical pheno-mena rigidly in terms of a physical theory, consciously denyinghimself the use of any other concepts; Lavoisier succeeded most

where he was the pragmatic chemist, least when (in his theory of

caloric) he in turn sought to bind physics and chemistry prema-turely in one. Despite electro-chemistry and other developmentsof the first half of the nineteenth century, this hiatus continued,

lasting throughout the formative period of modern chemistry.

Only in the third stage of chemical atomism, with the acceptanceof Avogadro's hypothesis after 1869 and the publication of the

periodic table did the reconciliation of chemistry and physics,

foreseen by Boyle, and partially abandoned by Lavoisier, becomean attainable objective.

CHAPTER XII

EXPERIMENTAL PHYSICS IN THEEIGHTEENTH CENTURY

tI

^HE dual character of eighteenth-century science has alreadyI been remarked upon. On the one hand, those threads which

-A. the historian of science has carefully followed through the

preceding hundred years tend to become dry and brittle; the ex-

citement had passed and there remained but its sequelae, a rather

timid experimentation and a cool, logical extension of what were

now commonplace ideas. The mood changed too. The rebellious

spirit of a Galileo was no longer necessary, for the works of Aris-

totle had passed out of serious science into the care- of classical

scholars, and the scientific revolutionaries were now respectablecitizens of the republic of learning. As the scientific movementbecame more comme ilfaut, so it acquired an element of dullness:

no one can be very interested in the sort of chemical experimentsthat Dr. Johnson performed to soothe his mind, in the lessons onmechanics that were arranged for the royal children, or in the

scientific pot-boilers ofJohn Wesley. As science became fashion-

able, patronage demanded that a major discovery be presented as

a humble tribute rather than as a challenge to established philo-

sophy. But these idiosyncrasies of a society which left Priestley

to the mercy of the Birmingham rabble and made Banks President

ofthe Royal Society, and in which the Ladies' Diary was filled with

mathematical conundrums, are not after all of the first importance.Nor was the England of Hume and Gibbon or the France of

Voltaire and Diderot immune to the challenge of intellect; and it

is obvious from what has gone before that in its science the

eighteenth century was by no means an age ofmere continuations,

for the creative drive was not so much weakened as altered in

direction.

On the other hand, therefore, new threads of rich interest

strengthened the texture of science in the eighteenth century.

Strategic advances were not made along the broadest paths, but

339


where the giants of the seventeenth century had been least suc-

cessful. This is strikingly apparent in physics. The natural heirs

of Newton were among the French school of mathematicians

D'Alembert, Clairaut, Lagrange, Laplace. The fundamental con-

cepts of mechanics were defined more neatly and exactly by them,while at the same time they moulded the mathematical structure

of the science into a beautifully complete and harmonious series of

equations. They achieved an elegance and precision in compari-son with which the work of the seventeenth century seems involved

and fumbling: even Newton's Principia, beside the MlcaniqueCtleste of Laplace, reveals a clumsy mathematical treatment. And

Laplace, unlike Newton, saw no reason to bring God into his

hypotheses. But the refinements of the French mathematicians

in no way modified the essential principles of mechanics, which

were already fixed, although their more penetrating analysis en-

abled some new problems to be solved, and some old errors to be

corrected. The many new and useful ideas that they put forward

must therefore be ascribed to the second order of discovery, as

being derivative rather than fundamental. At the same time, at a

lower level, experimentation in mechanics, pneumatics, hydraulicsand optics the organized departments of physical science was

taken up extensively. In Leiden Musschenbroek, in London the

Hawksbees, were already creating before 1710 a tradition of

demonstrative teaching. It is perhaps invidious to call their lec-

tures semi-popular, for the experiments they devised were often

far more ingenious and conclusive than those suggested by the

pioneer physicists. Such a work as Desagulier's Course of Experi-

mental Philosophy (1734 etc.) was a valuable manual of laboratory

practice and a sound introduction to physics without mathematics.

Concurrently there was a steady improvement in the design of

familiar instruments, such as the barometer, thermometer, hygro-

meter, air-pump, balance and so on; with these multitudes of

observations were performed, without, however, eliciting anymajor discovery. The situation in physics was clearly, so far as its

more highly organized departments were concerned, very different

from that in astronomy (for example), where Bradley's discoveryof the aberration of light was the direct result of refinement in

angular measure. Yet even so, problems of values arise, and it

cannot be taken for granted that the less dramatic work of the

eighteenth century had the less significance. It could be argued,

PHYSICS IN THE EIGHTEENTH CENTURY 341

for instance, that the graduated scales of Fahrenheit and Reaumuralone made thermometry effective in science, with importantresults in both physics and chemistry.

It is indeed very easy to undervalue second-order discoveries

in a period of consolidation. Creative ability of the first order is

extremely rare, and though its works must figure largely in anyshort account of the development of science, it would be absurd to

suppose that it could flourish apart from the context created bymen with smaller endowments. Between the peaks of scientific

achievement there is a time when activities are re-phased, when

perspectives alter, when with an enlarged range of facts the major

problems gradually modify their shape. Without this Newtoncould not have succeeded Galileo, nor Darwin Linnaeus. More-

over, it very rarely happens that the statement or the demon-stration of a first-order discovery are so perfect that they win

complete conviction, or that its potentialities are fully exploited.The task of welding the fabric of science together, of preservingthe logic and homogeneity which originality in its highest

degree often seems to imperil, usually falls to the derivative

investigator, and it is by this consolidation, as well as by its most

splendid feats of conceptualization and experiment, that science

grows.Two aspects of such consolidation are well illustrated in the

experimental physics of the eighteenth century. The expeditionto the head of the Gulf of Bothnia led by Maupertius and Clairaut

in 1736-7 was a bold undertaking for the time. Forests tangledwith fallen trees had to be penetrated, rapids navigated, and

quadrants handled when the mercury had sunk far below zero, bythese gentlemen fresh from the salons of Paris. Their purpose was

to measure the length of a degree of latitude, in order to comparetheir result with that already obtained in France by Picard. Uponthis comparison rested the verification of an important theory. For

if the degree proved to be longer in northern than in southern

latitudes, then the earth was flattened in the polar regions, as

Newton had reasoned from dynamical considerations. This provedto be the case, and the ratio of the polar to the equatorial diameter

of the earth was found to be 177/178. Some years later a similar

ratio was worked out from the results of another geodetic expedi-tion to Peru (1735-43). The critics of the Newtonian theory of the

earth's shape, including the astronomer Jacques Cassini, were


thus decisively confuted. 1 Newton's theory, however, gave the

ratio of flattening as 229/230. A much better agreement was

obtained in Clairaut's own reinvest!gation of the theory (1743),

which yielded a formula relating the earth's ellipticity to the

gravitational attraction at any latitude. 2By these means, not only

was the application of the principles of mechanics to the greatmass of the earth itself validated, but the actual method of apply-

ing them was improved to give a better coherence between theoryand experiment. At the same time, new light was thrown on the

pendulum experiments made in different parts of the globe. The

impregnability of Newton's theory of attraction was further in-

creased, at a time when it had still to win the confidence of manycontinental scientists.

The course of these events was predictable. It was certain that

if there was a controversy over the shape of the earth, it would be

settled by making measurements that was the established spirit

of the scientific revolution. It was also certain that if theory andmeasurement did not wholly coincide attempts would be made to

re-examine the theory in search of some neglected factor. Exactlythis happened and the theory was improved. In contrast, other

second-order discoveries in eighteenth-century physics, thoughcontinuations of what had gone before, were altogether unpre-dictable. Perhaps the most striking of them was made by the

London optician, John Dollond, in 1759. Newton had supposedthat when a beam of light passed through a prism, the dispersionof the colours in the spectrum cast was in an invariable proportionto the degree of refraction, and quite independent of the material

of the prism. Consequently he had held that chromatic aberration

(caused by the failure of lenses to bring all colours to the same

focus, owing to dispersion) was incapable of correction. TheGerman mathematician Euler, thinking of the human eye as a

perfect lens-system made up of several media, suggested that a

triplet "lens" formed by enclosing water between the interior

concave surfaces of two juxtaposed glass lenses would likewise be

free from aberration. He was able to work out (1747) the required

curvatures, but attempts to put his idea into practice failed.

1 Cf. Pierre Brunet: La vie et Vmwre de Clairaut, in Revue d'Histoire des Sciences ,

vol. IV (Paris, 1951), pp. 105-32.1 The theory was also revised a little earlier by the Scottish mathematician

Maclaurin using methods much less comprehensive than those of Clairaut.


Following Euler's suggestion, Dollond experimented on the rela-

tive dispersion and refractive power of water and glass, and later

of the two kinds of glass, crown and flint.1 He found that in a

"doublet," consisting of a convex lens of flint-glass and a concave

lens of crown-glass, the curvatures could be so adjusted that the

dispersions were nearly equal and opposite, while the greater re-

fraction of the flint-glass enabled the combination to behave as a

convex lens. An almost achromatic object-glass for telescopes was

possible: astronomers, who had been increasingly turning to the

reflecting telescope, were once more able to make use of the morereliable refractor. Attempts were made almost at once to applyDollond's discovery to the manufacture of achromatic objectivesfor microscopes, a task of which the solution occupied more than

fifty years. Perhaps most important of all, Newton's authority in

optics was seriously checked, almost for the first time. His confi-

dent belief, unfounded on experiment, was exposed as an error.

The principal innovations in eighteenth-century physics were,

however, in totally new directions, showing that the conceptual

fertility and experimental ingenuity so marked in the precedinghundred years were far from exhausted. Indeed, the two majorlines of advance were intrinsically far more difficult than those

hitherto followed. The seventeenth century had failed, for ex-

ample, both to place the science of heat on an exact quantitative

foundation, and to make the conceptual distinctions which were

essential to a true understanding of the phenomena. For these

the vague notions of corpuscularian philosophers that heat was'

nothing else but a very brisk and vehement agitation of the partsof a body* (Hookc) were a very unsatisfactory substitute. Even

Boyle had not been able altogether to renounce the idea of "fire

particles," or to distinguish firmly between combustion and other

manifestations of heat. Eighteenth-century physicists found it moreuseful to think of heat as a fluid (called caloric in the new chemi-

cal nomenclature), which flowed from hot bodies to cold; an

hypothesis which (like that of phlogiston) proved to be radicallymistaken but which served well at a certain stage.

In particular, this view of heat was extraordinarily appropriatesince most of the eighteenth-century experiments on heat were

concerned with thermal capacity and calorimetry. Measurementsof temperature by means of thermometers (though without regard

1Flint-glass contains a large proportion of lead, crown none.


to any widely accepted scale) had become fairly commonplaceafter 1660, but for a long time no distinction was made between

the temperature of a body, and the amount or quantity of heat

present in it. This was natural enough, for it was believed that

equal weights of all substances had the same thermal capacitythat is, if equal weights of water and iron were placed in the same

oven, they would both be raised to the same temperature in a

given time. Fahrenheit seems to have been the first to note a con-

trary observation. Comparing the heating and cooling effects of

equal volumes of water and mercury, he found that the latter was

not thirteen times as effective as the former, as the density-ratio

would suggest, but only 60 per cent, as effective! From this Black

judged (about 1760) that the amounts of heat required to raise

two different bodies through the same number of degrees of tem-

perature were in a very different proportion from that of their

densities (assuming the volumes to be equal). Black went on to

compare the amount of heat required to raise i Ib. of water

through t with that required to raise i Ib. of any other substance

through 7*, which could easily be done by mixing the two to-

gether at different temperatures so that they attained a commontemperature. From this experiment the relative heat-capacities

(or specific heats) of various substances could be ascertained,

taking that of water as a standard. 1 It was easy to imagine that

different substances had different capabilities for absorbing the

matter of heat (caloric), the association of the familiar notions

fluid and capacity proving as fruitful in the science of heat as it did

later in the science of electricity.

Black's other discovery concerning the capacity of bodies for

acquiring heat was even more surprising. The plausible notion

that when a solid (such as ice, or a metal) was brought to its

melting point as shown by a thermometer, only a small amount of

further heat was required to liquefy it had not been challenged.

Similarly it was thought that a minute loss of heat was enough to

cause water at 32 F. to congeal : no discontinuity between the

solid and liquid states, in relation to heat lost or absorbed, was

imagined. Black, however, observed that after a spell of cold1

e.g. mixing i Ib. of water at /, and i Ib. of mercury at T (T > t), the

resulting common temperature being x, the quantity of heat sufficient to

raise the mercury through (T x) has raised the water through (x /):whence the ratio of the thermal capacities of water and mercury is as (7* x)to (x

-t).


weather masses of ice and snow would last for weeks without

melting; were it not so 'torrents and inundations would be incom-

parably more irresistible and dreadful. They would tear up and

sweep away everything, and that so suddenly that mankind should

have great difficulty to escape their ravages.' A piece of melting

ice, he reasoned, must still be capable ofabsorbing a great quantityof heat, although the water running from it was at freezing-point.In other words, the ice was capable of taking up heat, without a

corresponding increase in temperature being apparent; the onlyeffect of this extra heat was the liquefying of the ice. It was latent,

because it seemed to be *

absorbed or concealed within the water,so as not to be discoverable by the application ofthe thermometer.'

Black then proceeded to measure experimentally the amount of

latent heat taken up by ice on its conversion into water, and bywater on its conversion into steam. Thus he attained the concep-tion of a definite quantity of the "matter of heat" insensible to

the thermometer being involved in any change of physical state;

this "quantum" of heat was not a mere agent dissolving ice into

water, but was a physical constituent of water differentiating it

from ice, or alternatively, from steam.

Later, Laplace and Lavoisier were able to perfect Black's ex-

periments with the ice-calorimeter which they invented. 1They

pointed out that such quantitative determinations could be

carried out without theoretical preconceptions, but, like Black,

they favoured the material theory, as is very evident in Lavoisier's

Traitt felementaire de Chimie. Like Black, they concluded that any

sample ofmatter (in a given physical state, at a given temperature)consists of substance and heat, the absolute degree of heat being

incapable of registration on a thermometer, and residing in all

bodies even at the lowest attainable temperatures. Their experi-ments went much further than Black's in studying the evolution

or loss of heat in chemical operations, whence it appeared that

the theory of chemistry would need to account not merely for

matter-reactions (syntheses, analyses, exchanges and so forth) but

for the heat-reactions with which these are integrally associated.

In modern terms, they had realized that questions of energy are

involved in chemical processes; as the concept energy was unknownto them, however, they naturally tended to make the heat-reaction

1 In this instrument, the quantity of heat lost by a body in falling to o C.

was measured by the weight of water melted from a surrounding jacket of ice.


cognate to the matter-reaction, by treating heat itself as a material

entity, and measurements of "quantities of heat" as measurement

ofsomething, which Would be conceived (at least in imagination) as

existing apart from the matter whose quantity of heat was

measured. The very obvious formulation

ice + heat -> water; water + heat -> steam

emphasized the dichotomy between the matter (water-corpuscles)identical in ice, water and steam, and the absorbed quantity of

something measurable making the distinction between its three

states. Attempts, throughout the eighteenth century, to measure

the mass of heat by weighing heated and cooled bodies, which hada negative result, did not disturb those who held that heat was a

weightless fluid. 1Only in 1798 was attention called to the fact

that bodies can evolve an indefinite amount of heat through fric-

tion by Benjamin Thompson's (Count Rumford) experiments. Onthe material theory the quantity of heat contained in a body at

a given temperature was limited absolutely, but in spite of this

difficulty, the kinetic view of heat (as it was less applicable, at this

stage, to any other phenomena than those of friction) failed to

displace the material theory for another half-century.This fact is itself enough to provoke reflection among those who

hold that quantitative experiments are infallible instruments of

scientific progress. When the theory of heat was entirely qualita-

tive, not to say speculative, in the seventeenth century, a more"correct" kinetic view prevailed. The material theory which so

successfully resisted, in the decade 1840-50, the attrition ofMayerand Joule was decisively established by the quantitative experi-ments of Black, Laplace, Lavoisier and others. The "correct"

kinetic view was in fact decisively obstructed by its failure to yield

neat and easily comprehensible quantitative results, and for this

reason it could not, perhaps, ever have been established save (as

it eventually was) under the cloak of a generalized concept of

energy.In many of its aspects eighteenth-century physics represents

the pre-history of this concept. Mechanical energy, as vis viva, andthe power to do work, was very attentively considered. The first

1 It is very strange that the implausibility of the concept of matter without

weight (which has been held by some to have inspired Lavoisier's attack on

phlogiston) was one which he himself embraced in his own theory of caloric.


steps towards the study of chemical energy were taken by Laplaceand Lavoisier. The very complex role of heat in physical andchemical changes was at least partially disclosed, and in a purely

practical way the connection between heat energy and mechanical

energy was of great interest to engineers, ever extending the utility

and efficiency of the steam-engine as a prime mover. The majorinvention of this period Watt's introduction of the separate con-

denser is said to have been inspired by Black's discovery of latent

heat, and certainly Watt carried on his own investigations into the

physics of heat. 1 It was clearly his purpose to squeeze the maxi-

mum mechanical value from the "quantity of heat*' contained in

steam and so cut down the coal bills of those who bought his

engine but the theoretical implications, in terms of a"perfectly

efficient" engine, were only worked out by Sadi Carnot about

1824. Heat energy in the form of invisible radiation was also

known, and the likeness in properties between this form of heat

and light was recognized. Experiments to find out whether light

itself has energy for if a beam of light consisted of a stream of

corpuscles travelling at a very high speed, their impact upon an

opaque surface should be detectable, even though very minute

yielded some positive effects, but these were most probably due to

other causes. Perhaps most important of all was the elucidation

of a new form of energy, electricity. Certainly this was the most

striking, the most original, and the most progressive branch of

eighteenth-century physics. The spectacle of the erect hair, the

nasal sparks, of an electrified youth hung in silk cords from the

ceiling excited the rather coarse humour of the age; the mysteryof lightning drawn off down an iron rod and confined, like a jinn,

in a Leyden bottle, was witness to the strange power of nature andman's intellectual mastery of it; while, at a more serious and

prosaic level, a new corpus of experimental and theoretical know-

ledge was taking shape, of incalculable importance for the future.

No one could have foreseen, in Franklin's day, the extent to which

1 It was not at all necessary, however, for Watt's purpose that the maincause of the wastefulness of contemporary steam-engines (the chilling of the

cylinder and piston by the injection of cold water to produce a vacuum) shouldhave been so scientifically diagnosed. An intuitive realization of the folly of

alternately heating and cooling the same masses of metal without any produc-tive purpose would have been amply sufficient. So that, whatever advice Wattmay have received from Black, it can hardly be said that the separate condenserwas an immediate fruit of the physics of heat.


physics was to become the science of electricity, yet already by1800 almost every experimental physicist was to some degree an

electrician.

All this grew from very humble origins. Gilbert had shown that

the attractive property of rubbed amber was quite widespread in

nature, and had coined such terms as "electric" (from Greek

elektron amber), and "charged body." Soon afterwards the

mutual repulsion of similarly charged fragments of light materials

was noticed for the first time. But the first hints of more remark-

able effects followed upon the introduction of the first electrical

machines, and thus anticipated the course of the later history of

electricity: every important step was brought about by some newinstrument or device. For electrical phenomena are not mademanifest in nature; the few that occur (such as lightning) could

never conceivably have been interpreted correctly in the light of

reason. They were entirely hidden from artisans and other prac-tical men skilled in nature's ways, no tools or instruments ot

science or art could be easily adapted to an inquiry into electricity,

and the human body is very limited in its reactions to electrical

stimuli from outside. There could, therefore, be no progress in

electrical science without means of creating charges, currents etc.,

and means of revealing their various properties. Theoretical

rationalization was bound to be, in the very early stages, of rela-

tively little importance, and in any case subject to extremely rapidfluctuations.

The first electrical machine was a globe of sulphur or glass,

mounted on an axle and rotated by a handle, which was rubbed

against the hand until highly electrified. The glow, visible in the

dark, produced by discharge between the globe and the hand was

first noted by Otto von Guericke, who also succeeded in trans-

mitting the electrical effect along a linen thread. Another curious

phenomenon observed at about the same time was for long unre-

lated to electricity. This was the luminosity in the vacuum of a

barometer when the mercury was shaken. Only in 1745 was it

shown that under these conditions the glass tube became electrified,

though Hawksbee, about 1710, had caused a similar glow to

appear upon an electrical machine worked in vacuo, and inside anexhausted vessel rubbed externally. Hawksbee allowed a chain

to hang against the globe of his electrical machine, so that the

charge would be taken to a large "prime conductor," but the next


improvement the use of a soft rubber instead of the operator'shand was only introduced a little before the middle of the

century.The study of conduction was taken further by Stephen Gray

(1732), who found that charges could be transmitted along, or

induced into, very long lines of thread when these were suitably

supported. He was thus led to make the fundamental distinction

between insulators and conductors, for silk filaments did not permithis charges to leak away, while equally fine copper wires did.

Hair, resin and glass proved like silk non-conducting. A, French-

man, Charles Dufay, had the ingenuity to mount a variety of

substances upon insulating supports in order to demonstrate that

all including the metals could be electrified by friction whenisolated from the earth; he saw that Gray's distinction between

insulators and conductors was really more primary than the

established one between electrics and non-electrics, to which it

had seemed analogous. Dufay, moreover, discovered that a frag-

ment of gold leaf, charged with an electrified glass rod, was not

repelled (as he expected) by a piece cf electrified amber, but

strongly attracted to it. The lesson, from magnetism, was obvious

enough; the two charges, the one "vitreous" and the other

"resinous." were of opposite sign. In the neutral state all bodies

contained equal quantities of both electricities; the action of fric-

tion was to remove a part of one or the other, leaving behind

a superfluity of the second.

Any substance could be charged on a suitable stand. A numberof experimenters tried to electrify water in insulating glass vessels:

they discovered, to their distress, that if with one hand graspingthe jar full of liquid, with the other hand they tried to take awaythe wire leading into it from the electrical machine, they ex-

perienced a frightful shock. They had, in fact, formed a condenser

and discharged it through their bodies: it was an easy step to

make the "Leyden jar" more convenient by lining it within and

without with metal foil and to learn to handle it with greatercaution. With the aid of powerful frictional machines, and the

large charge built up in a Leyden jar, it was possible by 1750 to

produce very striking sparks, and discharges heavy enough to kill

small animals or to be transmitted through long circuits of wire

or water. Attempts were even made to estimate the velocity of

the motion of a charge by the interval between two sparks across


gaps separated by a long circuit: but of course without success.

The heating effect ofelectricity (e.g. in melting fine conductors) was

easily perceived as were some of the effects associated with dis-

charge through a vacuum. Upon electrical theory the effect of the

discoveiy of the condenser was profound. The dualistic hypothesisof Dufay was clearly susceptible of simplification: it was unneces-

sary to suppose that there were two kinds of electricity (com-

parable to the two poles of a magnet) for "oppositeness" could be

taken, as in mathematics, as a difference in quantity rather than

a difference in quality. On such a view, with a normal charge a

body would be neutral, with an excess of electricity positively

charged, and with a defect of electricity negatively charged. This

view could be applied with particular success to the novel

phenomena revealed by the condenser.

The man who so applied and developed the unitary theory of

electricity was Benjamin Franklin (1706-90), retired printer of

Philadelphia, popular philosopher, later hero of the Americanrevolution and elder statesman of the young republic. With his

plain common sense and distrust of subtlety, Franklin combinedan active scientific imagination sharpened, perhaps, by his almost

complete ignorance (during the creative stages of his work) of

European theories. In his opinion, which strongly reflected the

corpuscularian ideas of the age, electricity was a fluid, consistingof particles mutually repelling each other, but strongly attractive

to other matter, which distributed itself uniformly as an "atmo-

sphere" about a body or connected system of bodies. Electrification

was a process whereby an excess of this fluid was collected upon a

particular body, such as a glass rod, by friction or other means, so

that it became positively charged; or removed from it so that it

became negatively charged. Franklin believed (mistakenly) that a

discharge was simply a transfer, often in the form of a unidirec-

tional spark, from a body more highly charged with the fluid to

one less charged; and the repulsion between two positively chargedcork balls was readily attributed by him to the repulsion between

the excess of electric particles. When Franklin became aware that

negatively charged bodies also repel each other, he encountered a

difficulty which his theory could not overcome. He fully realized

the importance of the deduction, from his fluid theory, that within

a closed system the quantity of electricity must be conserved: a

person, placed on an insulating stand, could collect a positive


charge upon a glass rod by rubbing it. but only by electrifying his

own body negatively to an equal degree, that is, by forcing

electricity from his body into the tube. By inverse reasoning from

the same principle Franklin explained the action of the condenser,for every addition of electricity to one of its surfaces produced a

corresponding loss (to earth) from the other, as shown by the fact

that the Leyden jar could not be charged unless one plate wasearthed. The total quantity of electricity in the jar was always

constant, only its distribution being modified by electrification

since a connection between the plates (under any conditions)ensured a return to the neutral state. Franklin regarded the

condenser as fully charged when all the electric "atmosphere"had been driven off the earthed plate, for then no more could be

added to the positive plate, since this would have increased the

total quantity present.

This theory, and the experiments intended to confirm it, of

which many were already familiar to European electricians, were

warmly welcomed, as indeed were all contributions to science

from the New World at this time. But at first Franklin's letters did

not carry conviction, nor did they have any very dramatic effect.

Strangely, it was a less creditable, but more showy, suggestionthat brought about his lionization. Many electricians had noted

the similarity between the electric spark and lightning and be-

tween the accompanying crackle and thunder, speculating on the

possible identity of the two effects; there was therefore nothing

very new in Franklin's similar speculation. He, however, hadnoticed particularly the powerful action of pointed conductors in"drawing off" a charge silently and conjectured that if thunder-

clouds were, as he supposed, positively charged, the fact could be

revealed by drawing electricity away to a high, pointed conductor.

Having described the experiment, he failed to execute himself

(for a variety of reasons, among which lack of courage was

certainly not one). It was first successfully performed in France,soon after the translation of Franklin's early letters was made.The well-known "Kite experiment" at Philadelphia was carried

out, with a like result, before news of the French attempts andof his own sudden fame as the tamer of lightning had reached

Franklin in America. Richmann, at St. Petersburg, was the first

"martyr" to the pursuit of this new branch of electrical

science.


Until the moment of Franklin's intervention (1746-55) elec-

tricians had been wholly preoccupied with qualitative effects.

Most of the material published had dealt with the description of

phenomena, which the experimenters had sought to explain in the

light of ad hoc hypotheses, each of them jejune in varying degreesand inadequate to explain all the facts. Franklin himself had not

sensibly modified this slate of affairs, for though his single-fluid

theory was more comprehensive than any other, it was not com-

pletely so, nor did it really rise above the phenomenalistic level of

his work. The revisions he introduced himself were sufficiently

serious for it to be classified (logically) as no more than a pro-visional working hypothesis. The investigation of new effects

continued to be ofsome importance as, for example, in the studyof induction, of the role of the dielectric in condensers, and of

pyro-electric phenomena but a more rigorous inquiry into the

quantitative aspects of electrical phenomena grew up alongside it

during the second half of the century. In accordance with the

general principle already mentioned (p. 237), the electrician's

apparatus, which had formerly been limited to the revelation of

the qualities of electricity, now began to be adapted to measure

quantities. An interesting instance of this is the elaboration, from

the pith-balls and gold-foils formerly employed to test for the

existence of charges, of the torsion-balance of Coulomb (c. 1 784)and the electrometer of Bennet (1787). Hitherto, though the

achievement of solid additions to knowledge and the ingenuity of

theorization must be duly recognized, experiment and thinkingin electricity had been amateurish, for the former had often

partaken of the nature of a parlour game, and the latter hadincluded much extravagance. The rapid success of Franklin,

starting almost from zero, is an indication as well of the super-

ficiality of the subject, as of his own ability. Now, however,electrical science began to acquire a more serious status as a

branch of physics.

Among the first to deny themselves the pleasure of declaringwhat electricity is, was Joseph Priestley. His precisely regulated

experiments on conduction contain the seeds of later ideas of

electrical resistance; like ,/Epinus a little earlier, he found that

the distinction between conductors and insulators was far fromabsolute. Priestley used the length of a spark-gap, across which a

discharge would jump instead of traversing a long circuit, as a


measure of the circuit's resistance. He repeated Franklin's experi-

ment to show that there is no charge inside an electrified hollow

vessel of metal, and deduced from it (by analogy with a familiar

theorem on gravitational attraction) the opinion that'

the attrac-

tion of electricity is subject to the same laws with that of gravita-

tion'

that is to say, it varied proportionately to the inverse squareof the distance. This was perhaps the first proposition about

electricity that could be formulated mathematically, and more-

over a prediction to which experimental verification could be

applied. This was done by Robison two years later (in 1769), byCavendish, and by the French engineer Coulomb. Cavendish

designed an ingenious apparatus by which one metal sphere could

be enclosed within another, with or without electrical contact

between the two, finding that the charge applied was invariablyconfined to the outer sphere. He ascertained that the electric

force must vary as the square of the distance within limits of

i per cent. Many other quantitative experiments (partially

anticipating the later work of Michael Faraday) were performed

by him about 1771-3, which with typical unconcern he kept

entirely to himself. He was the first electrician to adopt a standard

ofcapacity (a metal-covered sphere, 12*1 inches in diameter), with

which he compared the capacities of other bodies, stating these

as "inches of electricity/' that is as the diameters of spheres of

equal capacity, and to realize that the charge upon a conductor

is proportional to both its capacity and the "degree of electrifica-

tion" applied. By "degree of electrification" Cavendish under-

stood the extent to which the "electric fluid" was compressedinto a body, so that he approached very near to the later conceptof electrical potential. He also knew that the capacity of a con-

denser varies with the material of the dielectric, and made several

measurements of what Faraday was afterwards to name specific

inductive capacity. He measured the conductivity of a variety of

solutions in glass tubes, discovering that this was independent of

the size of the discharge passed through them. Considering that

he made use of crude pith-ball electrometers, and relied upon his

own senses to compare the violence of electric shocks, the numeri-

cal results he obtained were astonishingly good. All this work,

unfortunately, had no effect upon the subsequent progress of

electrostatics, as it was totally unknown. The inverse square law of

electric force was first demonstrated in print by Coulomb (1785),


in experiments one of which was similar to that of Cavendish,while others made use of Coulomb's torsion-balance for the direct

measurement of forces. These experiments in turn served as the

foundation for Poisson's mathematical study of electrostatic forces

in the early nineteenth century.The interval was marked by no important discoveries. This was

undoubtedly due in very large part to the sudden fascination of a

new set of phenomenalistic effects, wholly unsuspected, in which

electricity appeared in another of its Protean forms. Hitherto the

manifestations of electricity had been limited to two groups: (a)

shocks and sparks, (b) repulsions and attractions. To the first

group belonged, besides the laboratory effects, those of lightningand the torpedo or electric fish. No serious physiological study hadbeen made of the first group of effects it was merely known that

a shock produced violent muscular contractions, and followed a

more or less direct path through the body though the adminis-

tration of shocks was (like most other things) regarded as havinga medical value. Hence experimentation in electricity had been

practically confined to the exploitation of the attraction-repulsioneffect in a variety of different ways. This in turn had its influence

on theory. In the first place electricity was literally regarded as an

effluvium, a particulate atmosphere surrounding the charged body.

How, Newton had asked, can an electrified body 'emit an ex-

halation so rare and subtle, and yet so potent, as by its emission

to cause no sensible diminution of the weight of the electrick

body . . .?J1 Then again, the Abb Nollet (1700-70) had sup-

posed repulsion and attraction to be the work of outflowing and

inflowing streams of the electric fluid. Later in the century, the

analogy between electrical and gravitational attraction becomingmore obvious, the electric effluvium seemed as absurd as the gravi-tational effluvium of pre-Newtonian physicists, and "

action at a

distance" was accepted. Thus the theory of electricity passed

through various phases of mechanical explanation, much as the

theory of gravity had done in the seventeenth century, owing to

the focussing of attention upon its mechanical manifestations.

Just as the weightless fluid caloric was capable of mechanically

expanding bodies, so the weightless electric fluid was capable of

putting them in motion even of causing continuous rotation in

a light wheel. Mechanical analogies really justified the concept of

1Opticks, Query 22.


electricity as a fluid, whose particles were capable of action at a

distance, for electricity could flow along conductors, filling bodies

to their"capacity," and yet be impeded by "impermeable" sub-

stances. Borrowings from the languages and ideas of hydraulicsare indeed obvious; Cavendish's concept of electrical

"pressure"

showed how fertile they could be.

It is the nature of a fluid, even an elastic fluid, to flow, and the

study of "electrostatics" had actually embraced some investiga-

tion into the flow of electricity along conductors. But the effects

produced by the flow of charge (under the prevailing conditions of

experiment) were not striking as compared with the mechanicallyobvious effects of a static charge. The motion of electricity, re-

vealed by a spark or a shock, was in any case a transient event,

restoring the apparatus to a condition of electrical neutrality, so

that the phenomenon of electricity had always appeared to be

discontinuous, indeed so much so as to be almost adventitious.

Charges were immediately annihilated by conduction to earth,

and no perfectly insulating material was known. They were

formed only by the chance electrification of a cloud, or by the

discontinuous action of friction, which suggested that they were

mechanically produced. The appearance of all the known effects

depended upon the discontinuity in the movement of electricity,

leading to the accumulation of large static charges.The discovery of new manifestations of electricity was thus of

absorbing interest for a variety of reasons. These were not the

result of mechanical action, nor were they themselves mechanical

in nature. They were continuous, and they required no effort. In

the prevailing theory some segregating action was necessary to

bring about the conditions of electrification the fluid had to be

impelled from one body to another, leaving the former unnaturally

empty and making the latter unnaturally full so creating an un-

balanced state which nature herself sought to adjust at the first

opportunity. The new effects predicated no such positive action;

it was not necessary, in order to produce them, to build upmechanically an artificial "degree of electrification."

The differences between the new phenomena and the old were

sufficient, at first, to obscure the connection between them. About1 780, in the laboratory of the Italian anatomist Luigi Galvani

(1737-98) at Bologna, an assistant happened to notice that whenhe touched with his scalpel the crural neive of a frog's leg which


he was dissecting the muscles were violently contracted. It was

remarked that this occurred while a spark was being drawn from

an electrical machine placed on the same table. Galvani repeatedthe strange experiment, under the same conditions and with a like

result. He introduced many variants, all of which proved that the

experiment failed unless the operator was in electrical connection

with the nerve, and the frog's leg effectively earthed. From this

Galvani suspected that some sort of electrical circuit was involved

for muscular contractions were known to occur when discharges

were sent through dead animals even though the frog was not

directly linked to the electrical machine. Many experiments were

performed at this stage to gain conviction that the stimulus was

really electrical. The next major step was a successful demonstra-

tion that lightning flashes acted upon the limb in an identical

fashion when similar electrical connections were made to it. In the

course of these atmospheric experiments Galvani observed that

frogs hung from an iron lattice in his garden by brass hooks pene-

trating into the spinal marrow gave occasional convulsions. Once,

happening to press one of the hooks firmly against the iron, he sawimmediate contractions. At first he thought that these were due to

the escape to earth of some atmospheric electricity accumulated

in the frog. To test this suspicion he re-created the same condi-

tions indoors, placing the frog on an iron plate and pressing the

brass hook firmly against it. Still the convulsions occurred (1786).Other combinations of metals, or even a circuit through his own

body, or a homogeneous wire, with which he made a"conducting

arc" between nerve and muscle, had the same effect, but not in-

sulators. Again Galvani satisfied himself by elaborate experimentsthat the decisive circumstance was the existence of a path alongwhich electricity could flow.

Had he been a more enthusiastic electrician, Galvani mighthave inquired more fully into the curious situation in which a

spark from an electrical machine or Leyden jar could influence

a frog's leg insulated from it. Instead, after his discovery that the

spark was unnecessary provided that a direct connection was madebetween nerve and muscle, he abandoned that subject. At this

point two other lines of inquiry suggested themselves. He could

examine more carefully the nature of the electrical circuit, andthis he did in some detail, finding that some metals were less

effective than others in the conducting arc, that liquids could be


used, and that a single conductor was less effective than one made

up from two metals. But he did not attach great importance to the

bimetallic circuit, because convulsions were obtained with a single

conductor. He was therefore led to concentrate upon the second

line of inquiry, convinced as he was that Leyden jars, machines,thunderstorms and other familiar sources of electricity could be

excluded from his explanation of the phenomena, and that the

conducting arc was simply an ordinary conductor of electricity.

The physiology of the frog's reactions now drew his attention,

since it appeared that the mere electrical connection of nerve andmuscle was capable of causing the same contractions as the appli-cation of an electrical stimulus to these parts. In the former case

the electricity moving along the conductor must have been sup-

plied by the frog itself. To hypothesize further still, was not the

stimulus given by a nerve to a muscle always electrical, for (as he

said) 'the hidden nature of animal spirits, searched for in vain

until now, appears at last as scarcely obscure' it was electricity!

Prepared in the brain, and distributed by the nerves, this "animal

electricity" on entering the muscles caused their particles to at-

tract each other more strongly, and the fibres correspondingly to

contract. In the muscles also electricity was stored, as in a Leyden

jar, so that from a communication between them and a nerve

ensued the convulsions witnessed in his last series of experiments.Thus Galvani brought his electrical discoveries to a close byriding off on a physiological hobby-horse, abandoning physics in

order to debate how his new knowledge of animal electricity

might be applied to the cure of disease. Many other scientists

eagerly followed his example.An alternative and less dramatic interpretation would have

made the frog's leg merely a sensitive detector of an electric

current through the circuit linking nerve and muscle, as in Gal-

vani's first experiments, the stimulus for the convulsions being

always supplied by an external source of electricity. On this view,

little compatible at first sight with his later discoveries, Galvani

had not discovered a new example of animal electricity (alreadyfamiliar in electric fish) ;

he had invented a new electrical instru-

ment, and a new source of electricity in motion the bimetallic

conductor of his last experiments. This was the interpretation of

Galvani J

s work put forward by Alessandro Volta (1745-1827) of

Pavia in 1 792, about a year after the first account of them was


published. At first Volta had given credence to Galvani's own

explanation, hailing his discoveries as no less epoch-making than

those of Franklin. Gradually, however, Volta uncovered facts

which compelled him to differ from Galvani. The most delicate

electrometer revealed no electricity in animal tissues; to cause the

muscles to contract, it was only necessary to apply an electrical

stimulus to the nerves, and not to the muscles themselves; and to

create this stimulus a bimetallic junction was essential. 1Finally,

in a letter destined for the Royal Society, Volta asserted that the

frog's leg as prepared by Galvani was nothing other than a deli-

cate electrometer, and that most of the phenomena attributed to

animal electricity were 'really the effects of a very feeble artificial

electricity, which is generated in a way that is beyond doubt by the

simple application of two different metals.'

By this time [wrote Volta in November 1792] I am persuaded that

the electric fluid is never excited and moved by the proper action

of the organs, or by any vital force, or extended to be brought from

one part of the animal to another, but that it is determined and con-

strained by virtue of an impulse which it receives in the place wherethe metals join.

2

He had invented a new theory of contact electricity, and was

compelled, in its defence, to criticize the physiological views of

the wretched Galvani, who died in despair after some years of

futile controversy. Meanwhile Volta continued his experiments.He found that the metals whose contact caused a flow of electric

fluid could be arranged in a definite order, that other conductors

such as carbon had the same effect, and that any moist conductor,such as water, served to bridge the different metals as well as

animal tissues. By 1795 he had propounded the "law" that when-ever two dissimilar metallic conductors were in contact with each

other and a moist conductor, a flow of electricity took place. In

1 796 he demonstrated that the mere contact of different metals

produced equal and opposite charges upon them, made visible

by the electroscope. This was the first proof of the identity of

galvanic and frictional electricity, ofwhich Volta had always been

convinced. The charges, which appeared to be indefinitely pro-

curable, were positive or negative according to the order of the

1 Volta ascribed the effects obtained by Galvani with a single conductingelement to lack of homogeneity and other differences in the metal.

2Opere (Firenze, 1816), vol. II, pt. i, pp. 165-6.


metaJs used in the series which he had discovered earlier. 1 The

intensity of the effects produced was still minute, and Volta real-

ized that it could not be increased by multiplying the number of

bimetallic junctions so much was obvious from the distribution

ofcharges. The case was different when two or more pairs of metal

plates in contact were joined together, not directly or by use of a

third metal conductor, but by one of the moist conductors such

as salt water, either placed in cups into which the metal plates

were dipped, or soaked into cardboard discs inserted between each

bimetallic pair. In this arrangement (described by Volta in 1800)the intensity ofthe effects produced was proportional to the numberof the pairs of plates, so that Volta could charge condensers>

produce sparks, and give severe shocks. This "artificial electrical

organ"(which Volta compared to the natural electrical organs of

certain fish), electromotor, or pile ,as it was afterwards called, was

as he said like a feebly charged Leyden jar of immense capacity,for it would yield electricity continuously. The continuity of the

flow of electricity from terminal to terminal of the pile was par-

ticularly emphasized by Volta in his descriptive letter to the RoyalSociety; as there was no instrument suitable for the detection of

continuous currents, he had to quote his physiological sensations

in proofof their existence. The situation was paradoxical, but nonethe less real.

It seems clear that Volta, who was little interested in the

chemical effects associated with the passage of an electric current,

completely misunderstood the functioning of the single cells in

his pile. He regarded the "electric force" as originating from the

contact of two different metals, not from the reaction of these

with the inoist electrolyte between them. In modern theory the

voltaic cell consists (for example) of copper, electrolyte and zinc;

but to Volta himself the copper-zinc junction was the "cell,"

the source of electricity, and the electrolyte served merely to

connect these together without neutralizing the charges collected

on the metals. He was still thinking, essentially, in electrostatic

terms:

The action exciting and moving the electric fluid is not due, as is

falsely believed, to the contact ofthe humid substance with the metal;or at any rate it is only due to that in a very small degree, which may1

i.e. -|- Zn, Pb, Sn, Fe, Cu, Ag, Au, C . These experiments were onlymade possible by Volta's improvement of the electroscope in earlier years.


be neglected in comparison with that due to the contact of twodifferent metals, as all my experiments prove. In consequence the

active element in my electromotive apparatus, in piles, or in cups, or

in any other form that may be constructed in accordance with the

same principles, is the mere metallic junction of two different metals,

certainly not a humid substance applied to a metal, or included be-

tween two different metals, as the majority ofphysicists have claimed.

The humid layers in this apparatus serve only to connect the metallic

junctions disposed in such a way as to impel the electric fluid in one

direction, and to make this connection so that there shall be noaction in a contrary direction. 1

This theory did not long survive. As Nicholson pointed out in

1802, an electric current could be drawn from cells consisting

of one metal and two electrolytes, and by this time already the

work on the new form of electricity was assuming a markedlychemical character. Fabroni, in r 796, had observed the oxidation

of one of a pair of plates of different metals joined together andimmersed in water. Ritter had perceived that the order of the

metals in Volta's series was a chemical order that of their

exchange in solutions of their salts. Very soon after Volta's letter

of 1800 reached London, Nicholson and Carlisle, experimentingwith the first of his piles to be constructed in England, had, by

following up a chance observation, electrolysed water into oxygenand hydrogen. Solutions of metallic salts were rapidly decomposedby the same means. Even in the mid-eighteenth century chemical

changes had been effected by electrostatic discharges, so that a

way of proving yet more firmly the identity of frictional and gal-vanic electricity offered itself. It was certain that electrical forces

could bring about a chemical change; was the converse also true?

Humphry Davy asserted this boldly. In 1800 he pointed out that

the voltaic pile could act only when the electrolyte was capableof oxidizing one of the metal elements, and that the intensity of

its effect was directly related to the readiness of the electrolyte to

react with the metal. Six years later, in a Bakerian lecture, Davysaid:

In the present state of our knowledge, it would be useless to attemptto speculate on the remote cause of the electrical energy, or the

reason why different bodies, after being brought into contact, should

be found differently electrified; its relation to chemical affinity is,

1Opere, vol. II, pt. ii, p. 158; (written in 1801).


however, sufficiently evident. May it not be identical with it, and anessential property of matter?

For on Davy's view, in accord with his experiments on contact

electricity, in the simplest types of electrochemical activity an

alkali which receives electricity from the metal v/ould necessarily, on

being separated from it, appear positive; whilst [an] acid under similar

circumstances would be negative; arid these bodies having respect-

ively with regard to the metals, that which may be called a positiveand a negative electrical energy, in their repellent and attractive

functions seem to be governed by laws the same as the common laws

of electrical attraction and repulsion.1

Thus Davy held that the concept of affinity, upon the basis of

which the phenomena of chemical combination were explicable,was itself to be explained in terms of electrical forces or

"energies."

His prediction that electrolysis would prove to be a most valuable

tool of chemical analysis was well borne out in the following year

when, by this method, he isolated potassium from potash andsodium from common salt.

In the same lecture of 1806 Davy presented his electrochemical

theory of the voltaic pile. He thought that, owing to the opposite"electrical energies" of the metals used, decomposition of the

electrolyte occurred by the breaking down of its natural affinity,

as in a solution of salt (for example)*

the oxygene and the acid

are attracted by the zinc [plate], and the hydrogene and the

alkali by the copper [plate].' The production of electricity, whenthe plates were joined in a circuit, was continuous because the

chemical action, that is the solution of zinc in the electrolyte and

the evolution of hydrogen from the copper plate, was continuous:

'the process of electromotion continues, as long as the chemical

changes are capable of being carried on.' Davy also believed that

owing to the tension created by the electrically opposed metals,

the whole of the electrolyte was in a state of continual decompo-sition and recomposition. There were obvious defects in this

account, but it had the great merit of integrating in one hypo-thesis the facts of contact electricity, discovered by Volta, and the

facts of chemical change associated with the flow of electric

current through compound bodies. Evidently Davy realized that

the action of electrolysis and of the voltaic pile are essentially the

1Philosophical Transactions, 1807, PP- 33 > 39*


same, though the one requires an electric current to be applied,and the other yields a current. At the same time he recognizedthat electricity could be produced without chemical change, andchemical changes occur with which no electrical effects were

associated; therefore chemical changes could not be 'the primarycauses of the phenomena of GALVANISM.'

The scope of electrochemical theory was extended and defined

by the Swedish chemist J. J. Berzelius, whose first memoir ap-

peared in 1803. To pursue it farther would be to exceed the limits

of this volume. What may be noticed is the significance of the

sudden emergence of this young branch of science, electricity, as

a bridge between physics and chemistry. A situation in which

certain phenomena had been studied for their physiological

significance, then reinterpreted by a physicist, and finally taken

up by chemists, was absolutely unprecedented in science. The

still-mysterious unity of nature was once more vindicated. For

twenty years the chemical manifestations of electricity dominated

research almost as completely as its mechanical manifestations

had in the eighteenth century; it was not until about 1820, with

the work of Oersted and Faraday, that the mechanical effects of

current electricity (provided by the voltaic battery) attracted

attention. Similarly, and inevitably, the mathematical theory of

electric current was many years younger than that of electric

charges, since in each case the mathematical theory was developedfrom the quantitative measurement of mechanical effects. All

this was the fruit of the one crucial invention of the voltaic pile,

the battery as it was soon to be called, to which Volta was led

systematically from the first chance observations of Galvani. Thechemical effects of transient electrostatic discharges had aroused

little interest, whereas those ofcurrent electricity were spectacular.

They raised the question of the relationship between the thing

"electricity" or "electric fluid" and ordinary ponderable matter

in a new and challenging form. Not only did electricity appear

(in Davy's words) as 'an essential property of matter' this, after

all, in a different context, was the conclusion already drawn byFranklin and Dufay it was rather that electricity was an active

and determinant concomitant of matter without which, accordingto Davy and Berzelius, the chemical behaviour of the elementaryforms of matter would be inconceivable. It was a logical conse-

quence of the electrochemical theory that electricity was very far


from being a kind of discontinuous abnormality, of concern onlyto the curious electrician who took pains to disturb bodies from

their normal condition of comfortable neutrality. Electricity was

not an adventitious atmosphere, or other circumstance, like

humidity, which could be left out of account except for very

special circumstances. From being casual, the rapid progress of

ten years rendered it causal, having a function deeply involved

in the differentiation of the various species of matter. Within a

few more years the physicist was constrained to follow the chemist

in making necessary adjustments so that he too could own in

what sense electricity was "an essential property of matter,"thus commencing his long ascent to the truth that the concepts

"electricity" and "matter" are not complementary, but actually

inseparable. In short, through the electricians' research, the link

between the mathematical conception of matter, begun byNewton, and the empirical (or at least pragmatic) conception of

matter proper to chemistry, was at last indicated although it is

even yet far from being completely established.

CONCLUSION

MUCHmore has been learnt about Nature, from the struc-

ture ofmatter to the physiology ofman, in the last centuryand a halfthan in all preceding time. Of this there can be

no doubt. But the scientific revolution ends when this vastly de-

tailed exploration began, for it was that which made such investi-

gation possible. At this point, in the early nineteenth century, a

scientific paper on almost any topic is intelligible as a direct pre-cursor to research which still continues. With infinitely feebler

tools, but with the same insistence upon accuracy in observation,

the same confidence in quantitative experimentation, the same

enmeshing of theory, hypothesis and factual reporting which

philosophers then and now found so resistant to logical analysis,

men were tackling their problems as scientists today are tacklingfar more complex ones.

It has become almost a truism to assert that the developmentof natural science is the most pregnant feature of Western civiliza-

tion. With technology and this is hardly any longer an independ-ent characteristic it is the one product of the West that has had a

decisive, probably permanent, impact upon other contemporarycivilizations. Compared with modern science, capitalism, the

nation-state, art and literature, Christianity and democracy, seem

regional idiosyncrasies, whose past is full of vicissitudes and whosefuture is full of dark uncertainty. Each of these features of Western

civilization has made its contribution to the genesis of science, to

which perhaps their combination was essential, but one mayimagine that science can flourish after one or all of these has lost

its historic individuality. Indeed, that is already happening.Modern science was the offspring of a form of society which has

lasted some four hundred years, playing a dominant role in world

history; that form of society is now in dissolution, but it seems un-

likely that science will necessarily disappear with it. For this, morethan any other feature ofWestern society, has been the cause of the

changes that we witness, and this also will be the most powerfulinfluence on the moulding of a future society.

If this much or even a fraction of it be granted, it seems

364

CONCLUSION 365

unfortunate that we understand the genesis of modern science as

little as we do. The modern study of Nature alone has had a de-

termining effect upon the course of civilization, on history in its

political, economic and intellectual totality. The science of Egyptand Babylonia, China and India, Greece and Islam and medieval

Christendom had no such effect. The recovery of it by historians

contributes little in a positive way to the understanding of the rise

and decay of these societies, though such work does illuminate the

origins and peculiarities of modern science. Among the challengesto which these societies responded successfully, or failed to meet,the ubiquitous challenge of Nature was certainly one; but the

organized, conscious, rational response to it that we call science

was of minor importance. Because of this, because some of these

earlier strivings with Nature are continuously connected, andbecause all of them share certain common characters distinguish-

ing them from modern science, they may be grouped together as

intermediate between yet more primitive attempts to explain andmaster the mysteries of man's environment, and modern science.

We know that modern science emerged from this intermediate

stage, from which no other society than the recent western Euro-

pean was capable of escaping, and it is this emergence that we donot adequately comprehend.

Many questions have been cursorily handled in this book be-

cause satisfactory discussion would require a different and muchmore extensive treatment. Perhaps it is not possible yet. Little is

known about the immediate pre-history of the scientific revolu-

tion, which seems to demand a fundamental revision of the con-

cept of the Renaissance: the relationship (for example) between

Oresme and Leonardo, between Leonardo and Galileo, as meneach thinking about Nature in a different way, is still obscure.

Equally so are the relations of art, technology and science at this

critical period, though it is easy to frame hypotheses, and conse-

quently the whole problem of the connection between the changesin society and the concurrent changes in science is involved in

doubt, to all but the dogmatic Marxist. Above all, the crucial

question of the scientific revolution is seen through a veil which

philosophers have hardly begun to raise. Why do men committhemselves to one kind of proposition about Nature rather than

another? Why do they (in the absence of factual guidance) find

one type of statement more plausible than an alternative? Why


prefer discourses about corpuscular streams, to talk of spirits, whenthere is no evidence for either? Why believe (or not believe) in the

existence of the vacuum? Such questions are less relevant to the

understanding of recent science (though perhaps not wholly

negligible), but to the understandings of its origins they are vital.

Men's thoughts and actions were modified in ways that we simplycannot ascribe to the results of observation and experiment; bysuch standards, for example, the whole history of Cartesian science

is utterly incomprehensible.

Why do men reject one kind of science in favour of another?

Why in modern Europe alone did they move from the intermediate

to the modern stage? The answer cannot be simple, or single. It

requires psychological and philosophical insight, as well as a com-mand of the historical facts, to which we have as yet scarcely at-

tained, for the operation, the incidence, and the impact of the

creative intellect are almost unknown. We cannot rely only uponappeal to experiment, observation, measurement, or any other

over-simplification of the complex processes of science, to presentus with a solution to this problem. Still less hopeful is the economic

interpretation of the history of science, which seeks to tell us whymen sought for control over natural forces, but cannot explainhow they were able to acquire it. The economic motive may have

made their attitude to Nature less disinterested, but cannot alone

have changed its character. So, too, we recognize that precisionin measurement has been of great importance, that experimentis the touchstone of hypothesis, that to the percipient observer the

unexpected is always a fertile challenge. Yet many of the most

dramatic challenges in the history of science have issued not from

the unexpected, not from the spectrum that was oblong instead of

round, not from the frog's leg that jerked instead of remainingstill, but from the orthodox, the expected, the familiar pattern of

experience and thought. What predisposed men to struggle for the

moving earth, atomism, evolution, and so disturb the calm quies-cence of their time when no awkward barrage of fact enforced

their turbulence? For, contrary to the straightforward inductive

view of science, it has often happened that men have looked for

facts to demonstrate a theory, as Galileo, Boyle and Newton did,

without science being any the worse for that. Perhaps the finest

minds are capable of stretching far beyond the immediate war-

ranty of facts.

CONCLUSION 367

If we admit so much, we may admit more. If modern science is

not merely an elaborate digest of pointer-readings, then it is the

more obvious that the scientific revolution involved more than

the discovery of ways of making such readings and digesting theminto a coherent synthesis. In the growth ofmodern science creative

imagination, preferences, assumptions and preconceptions, ideas

of the relations of God and Nature, arbitrary postulates, all playedtheir parts. Here then is the crux; that we cannot write the full

history of science save by reflecting the operations of original

thought, which we do not understand; and that we cannot exclude

from science, which is rational, the influence of factors which are

irrational.

APPENDIX A

BOTANICAL ILLUSTRATION 1

CERTAINLY naturalistic representations, both botanical and zoological,

may be attributed to the medieval period but only to its beginningand end. Such are to be found in the Greek Codex Vindobonensis (fifth

century) or in the Latin herbal ofPseudo-Apuleius (seventh century) ;in

both, however, there is already evidence of degeneration from the best

Hellenistic models. They occur again in the works of miniaturists andother artists from the end of the fourteenth century onwards. Betweenthese periods formalism and symbolism flourished and 'it is safe to

assert that at the beginning ofthe thirteenth century scientific botanical

illustration reached its nadir in the west* (Blunt). The herbal was then

a mere uncritical catalogue, illustrated by figures which are purelyconventional and heavily stylized. Botanical knowledge revived underthe influence of the translators, as in the De Plantis of Albert the Great

(c. 1200-80), the Herbal of Rufinus (c. 1290) and the Buck der Natur

of Conrad von Megenburg (1309-74), all of which show occasional

evidence of fii-st-hand observation. Some originality is also shown in

utilitarian writings of the thirteenth century and later dealing with

hunting, falconry and agriculture. But the revival of naturalistic illus-

tration was wholly the work of the artist, during the first stages of the

Renais ance. Some of the best early representations of plants comefrom the brushes of Botticelli or the brothers van Eyck, as later fromDiirer and Leonardo. Manuscripts equally prove that it was the artist,

not the man of learning, who returned to the natural model. Some ex-

cellent figures, like those of Cybo of Hyeres, are purely decorative andhave no relation to the text they adorn. The almost contemporaryBurgundian school of illuminators and Italian artists developed in the

first years of the fifteenth century great technical and artistic skill in

the representation of plants, producing such masterpieces as the herbal

of Benedetto Rinio, prepared by Andrea Amadio, now preserved at

Venice. The earliest printed herbals, however, still maintained the old

stylized convention, seen for example in the English Crete Herball (1526).

Only with the work of Brunfels (Herbarwn viva iconcs, 1530-36, illus-

trated by Hans Weiditz) and ofFuchs (Historia stirpium, 1542, illustrated

by Albrecht Meyer) was naturalistic interpretation transferred to the

wood-cut block.

1 Cf. Charles Singer: From Magic to Science (London, 1928); and "The herbalin antiquity and its transmission to later ages," J. Hellenic Studies> vol. XLVII,1-52; Wilfrid Blunt: The Art of Botanical Illustration (London, 1950).

369


APPENDIX B

COMPARISON OF THE PTOLEMAIC ANDCOPERNICAN SYSTEMS

THE geometrical equivalence of the geostatic and heliostatic methods

of representing the apparent motions of the celestial bodies, adopted by

Ptolemy and Copernicus respectively, is not often clearly emphasized-. though it is vital to any discussion of

the nature of the change in astro-

nomical thought effected by Coper-nicus. In a simplified form it may be

easily demonstrated.

Upper Planets (Fig. u). On the

Copernican hypothesis, O is the

place of the sun, B that of the earth

which has revolved through anyangle COB, and D that of a planetwhich in the same time has revolved

through the angle COD. The appar-ent position of the planet is on the

T. TM- TT line BD. Transposing this into Ptole-Fio. ii. The Upper Planets. . ~\ ,

5 ~ , , A*r maic terms, O is the fixed earth, Athe sun, and D the centre of the planet's epicycle. If F is the place of

the planet in the epicycle, then DF:DO = BO:DO. Moreover, AOBis a straight line, and /.FDO = /.COB /.COD = /.BOD. Theserelations follow from the form of the

constants used by Ptolemy and Co-

pernicus respectively (p. 15). Thusthe apparent position of the planetis given as before, since the line FOis parallel to BD, and the triangles

AFO, BDO, are identical.

Lower Planets (Fig. 12). Here the

situation is slightly different. The

Copernican representation is similar

to that given above, with the sun at

O, earth at B, planet at D, and the

position given by the line BD. Onthe Ptolemaic representation the

central earth is at O, the sun at A,and the centre of the planet's epicycle is located on the radius AO.Values for the radii of the deferent and epicycle may be chosen so that

D'F:D'O = DO:BO, provided that D'F + D'O<AO = BO. As be-

FIG. 12. The Lower Planets.

APPENDIX B 371

fore, these relations follow from the form of the constants adopted by

Ptolemy and Copernicus. For the same reason the velocity of rotation of

F about D' is such that /.OD'F = /.COD zLCOB= /_EOD. Thusit follows (as with the upper planets) that FO and BD are parallel, andthat the maximum elongation of the planet from the sun is the same on

either hypothesis.It may be noted that since any geometrical complexity added to one

representation may be duplicated by a corresponding one in the other,

the apparent positions of the planets are always the same on either

hypothesis. In the case of the inferior planets, Venus and Mercury,

however, the triangles OD'F, BOD, are similar but not identical.

These planets cannot appear on the Ptolemaic hypothesis, as they do on

the Copernican, on the remote side of the sun from the earth. On the

latter hypothesis, but not on the former, Venus should appear in quad-rature with the sun at maximum elongation. This fact was observed

by Galileo with the telescope. A simple adjustment to the Ptolemaic

system (proposed long before) made it identical with the Copernican in

this respect by centring the epicycles of Venus and Mercury upon the

sun, i.e. drawing them about A.

APPENDIX C

SCIENTIFIC BOOKS BEFORE 1500

WITHOUT compiling any very elaborate statistics, it is apparent fromthe work of A. C. Klebs ("Incunabula Scientifica et Medica," Osiris,

vol. IV, 1938) that the printed literature of science at the beginning of

the sixteenth century was in the main dominated by its established

traditions. Klebs lists more than 3,000 editions of 1,044 titles by about

650 authors. Among these occur 95 editions (and collections) of worksattributed to Aristotle, 18 editions of the Natural History of Pliny the

Elder, 7 of Ptolemy's Cosmographia (but none of the Almagest), and 5 of

Lucretius. Of ancient medical writers, Dioscorides (De materia medico)was printed twice, and Calcn (complete so far as known) once. But

separate works of both Hippocrates and Galen were included in num-erous collections ofmedical authorities. Celsus (De medicina) was printedfour times. Collections of classical writers on military affairs, agricul-ture and astronomy were popular enough to justify more than oneedition. Euclid was printed twice only.

Translations from the Arabic were often printed. They include

Avicenna's Canon of Medicine (14 editions) and the works of other greatIslamic physicians: al-Razi (15 editions besides titles in collections),Mesue (19 editions) and Serapion (4 editions). Averroes* commentaries


on Aristotle were well known in print, but not Arabic astronomical

writings.

Works deriving from the Latin West before 1400 form a very numer-ous group. The long-used Etymologic of Isidore of Seville was printed 8

times. An early product of the renaissance of learning in Europe, the

Quastiones Naturales of Adelard of Bath, merited 2 editions. Works by,or attributed to, Albert the Great were immensely popular, especiallythe Secreta mulierum and the Liber aggregations , amounting to 150 edi-

tions. Thomas Aquinas appeared in 17 editions and numerous collec-

tions, Albert of Saxony in eleven. Two more sought-after books werethe Sphere of Sacrobosco (3 1 editions) and the Physiognomia of Michael

Scot (21 editions). Less well known medieval treatises, like those of

Oresme (3), Thomas Bradwardine (3) or Walter Burley (5) all found

publishers. The most widely read English author was undoubtedlyBartholomew (De proprietatibus reruni) with 12 editions in Latin, 8 in

French, and others in English, Spanish and Flemish. Some medical

writers of the middle ages were still in demand for study, to judge from

the 31 editions ofArnald of Villanova, the 13 ofGuy de Ghauliac, andthe 9 ofMondino. The most popular of all medical treatises was still the

Regimen sanitatis of Salerno (41 editions). With these the 35 editions of

printed herbals before 1500 may be linked.

The proportion ofscientific books printed in the vernacular languageswas small, but it was a microcosm of the whole. The German languagewas perhaps the best endowed in this way, and next French; in Italy,

probably, the university tradition was too strong to render such ver-

nacular printing profitable, and the literate class in fifteenth-century

England did not at first demand many serious books. Many were of an

ephemeral nature prognostications and predictions, almanacks, and

popular treatises on the maintenance of health. This last group in-

cludes the Livre pour garder la sante (1481), and the German Regimensanitatis zu Deutsch (1472). Caxton printed The Gouvernayle of helthe in

1489. A book even more full of marvels than Bartholomew's, and

equally widely available, was Mandeville's Itinerarius (in English,

French, German, Italian and Flemish). Herbals were soon madeaccessible to the vernacular reader (German and French 1486, English

1525), as were treatises on anatomy deriving from Mondino (German,Hieronymus Brunschwig, 1497; Italian and Spanish, Johannes de

Ketham, 1493 and 1494). The Chirurgia of Guy de Chauliac was repre-sented in three languages before 1500. There were also some vernacular

books on reckoning.

Here, then, is evidence drawn from two dissimilar sources enforcingthe same conclusion. On the one hand, the great Italian printing-

houses, supplying a highly literate and academic market, found it

profitable to publish many of the "classics" of medieval science, often

APPENDIX C 373

in several editions; on the other hand, vernacular printing shows the

same intellectual content scaled down and vulgarized. There was no

sudden craving for originality, no epidemic of criticism. This is also

apparent from Mr. H. S. Bennett's study of early English publications

dealing with science and medicine (English Books and Readers, 1475-

1557, Ch. vi). The first surgical texts in English were based on Johannesde Vigo and Guy de Ghauliac; the first anatomy text (by Thomas

Vicary, 1548) on Mondino. Caxton's Myrrour of the World (1481) 'is a

typical example of the encyclopaedia beloved of the Middle Ages, andhere made available to the ordinary reader with no attempt to bringit up to date.' Yet it was reprinted in 1490 and 1529. Such works, Mr.Bennett writes: 'contributed little or nothing that was new. Their

compilers were content to reproduce knowledge that had been current

for centuries, and the stationers traded in these wares confident that

their customers would not be put off by their old-fashioned con-

tents.' (But were the customers conscious that the contents were old-

fashioned?) Caxton made no greater effort to revise the geographical or

historical knowledge which he imparted in his books, much of it taken

directly from the thirteenth and fourteenth centuries. In short, so far

as the respective tastes of printers, students and the general public maybe ascertained, they were conservative; those texts which had been

most in demand before the invention of printing were the very ones

that became most widely disseminated after it. Printing, therefore, had

comparatively little immediate effect on the literature of science in the

way of substituting novelties for traditions, though it did condemn to

darker oblivion those texts which were already half-forgotten by the

mid-fifteenth century, and, by reason of this, it reveals the strength of

the conservative forces extant in the early stages of the renaissance.

BIBLIOGRAPHICAL NOTESSTUDIES on the history ofscience are already so numerous that it is only possiblein these notes to give some indications of indebtedness, and of some possiblelines of exploration. I restrict myself here mainly to the English and French

languages, though these are (obviously) far from containing everything of

importance.

General: The journals Isis and Osiris, Annals of Science, Archives Internationales

d'histoire des Sciences (continuing Archeion), and Revue d'histoire des Sciences , are

indispensable. The bibliographies in Isis analyse work in the history of science

during the last forty years; cf. also G. Sarton, A Guide to the History of Science

(Waltham, Mass., 1952), and the handlist published by the Historical Associa-

tion (Helpsfor Students of History , No. 52). The period covered by this volume is

treated in all the general histories of science (Singer, Dampier, Wightman,Mason etc.) and especially by Professor H. Butterfield, The Origins of ModernScience (London, 1949), and H. T. Pledge, Science since 1500 (London, 1939).A. Wolf, History of Science, Technology and Philosophy in the Sixteenth, Seventeenth and

Eighteenth Centuries gives many valuable scientific details but is very deficient in

interpretation.

CHAPTER I

For reference and bibliography, G. Sarton, Introduction to the History of Science

(Baltimore, 1927-48, 5 vols.) and Lynn Thorndike, History of Magic and

Experimental Science (New York, 1 923-4 1) are essential. There is no fully adequate

short history for the medieval period. For Islam, cf. H. J. J. Winter, Eastern

Science (London, 1952), A. Mieli, La Science Arabe (Leiden, 1938). Some of the

older books, e.g. C. Singer, From Magic to Science (London, 1928) are still useful.

A. C. Crombie, From Augustine to Galileo (London, 1952) and Robert Grosseteste

and the Origins of Experimental Science (Oxford, 1953), takes a favourable viewof the medieval contribution to the scientific revolution, with much biblio-

graphical information. G. H. Haskins, The Renaissance of the Twelfth Century

(Cambridge, Mass., 1928), and Studies in the History of Medieval Science (Cam-bridge, Mass., 1924) ; J. Huizinga, The Waning ofthe Middle Ages (London, 1924) ;

H. Rashdall, Universities of Europe in the Middle Ages (ed. Oxford, 1936), are

useful for background. Editions of texts are being published in quantity, e.g.

E. A. Moody and M. Clagett, The Medieval Science of Weights (Madison, 1952);L. Thorndike, The Sphere of Sacrosbosco (Chicago, 1949), and The Herbal of

Rufinus (Chicago, 1946).

CHAPTER II

(a) There are geneial histories of medicine by F. H. Garrison (Philadelphia,

1929) and A. Castiglioni (New York, 1947) the latter has the more synthetictreatment. A valuable survey is C. Singer, The Evolution of Anatomy (London1926^ J. B. de C. M. Saunders and C. D. O'Malley,/!m/ru Vesalius (NewYork,

375


1950) give the anatomical illustrations with short notes. Cf. also C. Singer,

Vesalius on the Human Brain (London, 1952) the only translation of a fair

portion of De Fabrica; H. Gushing, A Bio-bibliography of Andreas Vesalius (NewYork, 1943); S. W. Lambert et al.

yThree Vesalian Essays (New York, 1952);

Saunders and O'Malley, and Singer, in Studies and Essays . . . offered to George

Sarton (New York, 1946), articles in the Bull. Hist. Med., vol. XIV, 1943;

J. P. McMurrich, Leonardo da Vinci the Anatomist (London, 1930), Vittorio Putti,

Berengario da Carpi (Bologna, 1937); G. Keyncs, The Apologie and Treatise of

Ambroise Part (London, 1951); Sir C. Sherrington, The Endeavour ofJean Fernel

(Cambridge, 1946).

(b) The edition of Ptolemy which I have found most accessible is that of the

Abbe Halma (with French translation, Paris, 1813-16), and for Copernicus the

original printing of 1543. Secondary works are: A. Armitage, Copernicus',the

Founder ofModern Astronomy (London, 1938), H. Dingle in The Scientific Adventure

(London, 1952), J. L. E. Dreyer, History ofPlanetary Systemsfrom Thales to Kepler

(Cambridge, 1906), F. R.Johnson, Astronomical Thought in Renaissance England

(Baltimore, 1937), E. Rosen, Three Copernican Treatises (New York, 1939), D. W.

Singer, Giordano Bruno, his Life and Thought (London, 1950), D. Stimson, The

Gradual Acceptance of the Copernican Theory (New York, 1917).

(c) Metallurgy and industrial chemistry are dealt with in G. Agrlcola, De re

metallica (trans. H. C. and L. H. Hoover, New York, 1950); C. S. Smith andM. Gnudi, T/ie Pirotechnia of Vannoccio Biringuccio (New York, 1943), C. S.

Smith and A. Sisco, Treatise on Ores and Assaying of I^izarus Ercker (Chicago,

1951). On history of pharmacology, E. Kremcrs and G. Urdang, History qf

Pharmacy (Philadelphia, 1940).

CHAPTER III

There is no wholly satisfactory English work on Galileo. J. J. Fahie, Galileo, his

Life and Works (London, 1903) is uncritical and out of date. F. Sherwood Taylor,Galileo and the Freedom of Thought (London, 1938) is better but limited. In trans-

lation there are Dialogues concerning Two New Sciences (H. Crew and A. de Salvio,

New York, 1914, 1952), Dialogues on the Two ChiefSystems of the World (T. Salus-

bury, London, 1667; S. Drake, California, 1953). Pierre Duhem's classic fitudes

sur Leonard de Vinci (Paris, 1906-13) and Origines de la Statique (Paris, 1905-6)are invaluable. Cf. also L. Cooper, Aristotle, Galileo

9and the Leaning Tower of

Pisa (Ithaca, 1935), Ren6 Descartes, Oeuvres (ed. Ch. Adam and P. Tannery(Paris, 1897-1913), R. Dugas, Histoire de la Mtcanique (Neuchatel, 1950), G.

Galilei, Opere, ed. A. Favaro (Firenze, 1890-1909), A. Koyr, jStudes GaliUennes

(Paris, 1939; ActualiUs Scientifiques et Jndustrielles Nos. 852-4 most impor-

tant), E. Mach, Science of Mechanics (Chicago, 1907), A. Maier, Die Vorlaufer

Galileis in 14. Jahrhundert (Rome, 1949) and Die Impetustheo*ie (Rome, 1951),R. Marcolongo, "Lo sviluppo della meccanico sino ai discepoli di Galileo*' in

Atti d. R. Ace. dei Lincei (Physical Series) vol. XIII (Rome, 1920), A. Midi, "II

Tricentario dei 'Discorsi e Dimostrazioni Matematiche* di Galileo Galilei"

in Archeion y vol. XXI (Rome, 1938) critical of Duhem etc., N. Oresme, "LeLivre du Ciel et du Monde" in Medieval Studies, vols. III-V (1941-3), G.

Sarton, "Simon Stevin of Bruges" in Isis. vol. XXI (1934).


CHAPTER IV

In addition to works already mentioned, A. Armitage, "The Deviation of

Falling Bodies," Ann. Sci., vol. V (1947), I. Bouiliau, Astronomia Philolaica

(Paris, 1645)^. L. E. Dreyer, Tycho Brake (Edinburgh, 1890), Joharm Kepler,Gcsammelte Werke (Munich, 1938-), S. I. Mintz, "Galileo, Hobbes, and the

Circle of Perfection," his, vol. 43 (1952), D. Shapley, "Pre-Huygenian Observa-tions of Saturn's Rings," his, vol. 40 (1949).

CHAFFER VThe best study is H. P. Bayon, "William Harvey, Physician and Biologist," Ann.

Sci., vols. Ill, IV (1938-9). General books are F.J. Cole, Early Theories ofSexual

Generation (Oxford, i93o),J. Needham, History of Embryology (Cambridge, 1934),E. Nordenskiold, History of Biology (New York, 1946), C. Singer, History of

Biology (New York, 1950). Cf. also H. Brown, "John Denis and Transfusion of

Blood, Paris, 1667-8," Isis, vol. 39 (1938), L. D. Cohen, "Descartes and Moreon the Beast-Machine," Ann. Sci.* vol. I (1936), C. Dobell, Antony van Leeuwen-

hoek and his "Little Animals" (London, 1932), G. Keynes, "The History of Blood

Transfusion," Science News, vol. Ill (1947), A. van Leeuwenhoek, Collected

Letters (Amsterdam, 1939-), W. Pagcl, "William Harvey and the Purpose of the

Circulation," Isis, vol. 42 (1951), C. E. Raven, John Ray (Cambridge, 1950),F. Redi, Opere (Napoli, 1778, Milano, 1809-1 i),J. Trueta, "Michael Servetus

and the Discovery of the lesser Circulation," Tale Jo. ofBiol. and Med. tvol. XXI

(1948), R. Willis, Works of William Harvey (London, 1847).

CHAPTER VI

There is to my knowledge no complete history of scientific method. Useful

contemporary studies are R. B. Braithwaitc, Scientific Explanation (Cambridge,

!953) M. R. Cohen and E. Nagel, Introduction to Logic and Scientific Method

(London, 1934), S. Toulmin, Philosophy of Science (London, 1953). Cf. also F. H.

Anderson, Philosophy of Fronds Bacon (Chicago, 1948), A. G. A. Balz, Cartesian

Studies (New York, 1951)? E. A. Buitt, Metaphysical Foundations of .Modern Physical

Science (London, 1925), A. C. Crombie and H. Dingle, op. cit. for Chs. I and

II, A. Gewirtz, "Experience and the non-mathematical in Descartes," Jo.Hist. Ideas

yvol. II, 1941, E. Gilson, La Philosophic au Moyen Age (Paris, 1944),

J. H. Randall, "The Development of the Scientific Method in the School of

Padua," Jo. Hist. Ideas, vol. I (1940), B. Russell, History of Western Philosophy

(London, 1946).

CHAPTER VII

(a) An excellent survey is M. Oinstein, The R6U of Scientific Societies in the i?th

Century (Chicago, 1938). Cf. also J. Bertrand, L'AcacUmie des Sciences et les

Academiciens de t666 d 1793 (Paris, 1869), T. Birch, History of the Royal Society

(London, 1756), H. Brown, Scientific Organization in i?th Century France (Balti-

more, 1934), A. Favaro, "Documenti per la Storia dell Accademia dei Lincei,"

Bullettino di Bibliografia e di Storia delle Science, vol. XX (Rome, 1887), A. J.

George, "The Genesis of the Academic des Sciences," Ann. Sci., vol. Ill (1938),F. R. Johnson, "Gresham College: Precursor of the Royal Society," Jo. Hist.

Ideas, vol. I (1940), R. F. Jones, Ancients and Moderns CSt. Louis, 1936), R.


Lenoble, Mersenne ou la Naissance du Mtcanisme (Paris, 1943), Sir H. Lyons, The

Royal Society (London, 1944), Notes and Records of the Royal Society, passim,

(b) A very important essay, with full references, is M. Boas, "The Establishment

of the Mechanical Philosophy," Osiris, vol. X, 1952. Also, H. Brown, "The Util-

itarian Motive in the Age of Descartes," Ann. Sci., vol. I (1936), R. K. Merton,

"Science, Technology and Society in iyth Century England," Osiris, vol. IV

(1938), G. Milhaud, Descartes Savant (Paris, 1921), J. F. Scott, The Scientific

Work of Rene" Descartes (London, 1952), P. Mouy, La Developpement de la Physique

Carte'sienne (Paris, 1934), J. R. Partington, "Origins of the Atomic Theory,"Ann. Sci., vol. IV (1939).

CHAPTER VIII

M. Cantor, Vorlesungen uber Geschichte der Mathematik (Leipzig, 1880-1908), is

still essential for reference. J. E. Montucla, Histoire des Mathematiques (Paris,

1 799- 1 802) is well worth reading on the seventeenth century. Cf. alsoD. E. Smith,

History of Mathematics (New York, 1923), and more popular accounts by E. T.

Bell, A. Hooper and others. M. Daumas, Les Instruments Scientifiques aux //* et

18* Siecles is excellent. The only good history of a single instrument is R. S.

Clay and T. H. Court, History of the Microscope (London, 1932). Further, I. B.

Cohen, "Roemer and Fahrenheit," his, vol. 39 (1948), J. W. Olmsted, "The

Application of Telescopes to Astronomical Instruments," Isis, vol. 40 (1949),

L. D. Patterson, "The Royal Society's Standard Thermometer," Isis, vol. 44

(1953), F. Sherwood Taylor, "The Origins of the Thermometer," Ann. Sci.,

vol. V (1947)-

CHAPTER IX

The best recent biography ofNewton is that of L. T. More (London, 1 934) ,which

does not wholly supplant Sir D. Brewster's Memoir (Edinburgh, 1855). Other

sources: E. N. da C. Andrade, "Robert Hooke," Proc. Royal Society A, vol. 201

(1950), A. Armitage,"

'Borrell's hypothesis' and the Rise of Celestial Mechan

ics," Ann. Sci., vol. VI (1948-50), A. E. Bell, Christian Huygens and the Develop-

ment of Science in the Seventeenth Century (London, 1947), W. J. Greenstreet (ed.),

Isaac Newton, Memorial Volume (London, 1927), R. T. Gunther, Early Science in

Oxford, vols. VI-VIII, X, XIII (Oxford, 1930-8), W. G. Hiscock, David

Gregory, Isaac Newton and their Circle (Oxford, 1937), History of Science Society,Isaac Newton (London, 1928), A. Koyre*, "La Me*canique Celeste de J. A.

Borelli," Rev. d 9

Hist. des Sciences, vol. V (Paris, 1952) and "An UnpublishedLetter of Robert Hooke to Isaac Newton," Isis, vol. 43 (1952), T. S. Kuhn,"Newton's *3ist Query* and the Degradation of Gold," his, vol. 42 (1951),E. F. MacPike, Correspondence and Papers of Edmond Halley (London, 1937),L. D. Patterson, "Hooke's Gravitation Theory and its Influence on Newton,"Isis, vol. 40 (1949), Royal Society Newton Tercentenary Celebrations (Cambridge,1947), E. W. Strong, "Newton and God," Jo. Hist. Ideas, vol. XIII (1952),H. W. Turnbull, James Gregory Tercentenary Volume (London, 1939), A. H.

White, Memoirs of Sir Isaac Newton's Life by William Stukeley (London, 1936).The best editions are those of the Principia by F. Cajori (Berkeley, 1946) and of

the Opticks (London, 1931). The Oeuvres Computes of Christiaan Huygens (LaHaye, 1888-1950) are invaluable for reference.


CHAPTER XTo the books listed for Ch. V may be added: A. Arber, Herbals (Cambridge.

1950), P. G. Fothergill, Historical Aspects of Organic Evolution (London, 1952,with full bibliography), Knut Hagberg, Carl Linnaus (London, 1952), W. P.

Jones, "The Vogue of Natural History in England, 1 750-70," Ann. Sri., vol. II,

1937, C. E. Raven, English Naturalists from Neckam to Ray (Cambridge, 1947),and Natural Religion and Christian Theology (Cambridge, I953),C. Singer, "TheDawn of Microscopical Discovery," Jo. Roy. Microscopical Soc. (1915).

CHAPTER XI

There is no modern history of chemistry on the large scale. J. R. Partington,Short History of Chemistry (London, 1948) is an excellent introduction. Cf. also,

on industrial chemistry, A. and N. Clow, The Chemical Revolution (London, 1952);L. J. M. Coleby, The Chemical Studies ofP. J. Macquer (London, 1938), P. George"The Scientific Movement and the Development of Chemistry in England,"Ann. Sci., vol. VIII (1952),^ S. Kuhn,

" Robert Boyle and Structural Chem-

istry in the i7th Century," Isis, vol. 43 (1952), D. McKie, Antoine Lavoisier

(London, 1935), and Essays ofJean Rey (London, 1951), and "Black's Chemical

Lectures," Ann. Sci., vol. I (1936), H. Metzger, Les Doctrines Chimiques en France

du debut du rf a la fin du 18* Sticle (Paris, 1923) and Newton, Stahl, Boerhaave et la

Doctrine Chimique (Paris, 1930), L. T. More, Life and Works of Robert Boyle

(London, 1944), J. R. Partington, "Joan Baptista van Helmont," Ann. Sci. y

vol. I (1936), and with D. McKie, "Historical Studies in the Phlogiston

Theory,"^wi. Set., vols. II-IV (1937-9), T - s - Patterson, "Jean Beguin and his

Tyrocinium Chemicum," Ann. Sci., vol. II (1937), and "John Mayow in Con-

temporary Setting," Isis 9 vol. 15 (1931), J. M. Stillman, The Story of Early

Chemistry (New York, 1924), J. H. White, History ofthe Phlogiston Theory (London,

1932).

CHAPTER XII

P. Brunet, L'Introduction des Theories de Newton en France au 18* Siecle (Paris, 1931),I. B. Cohen, Benjamin Franklin's Experiments (Cambridge, Mass., 1941 with

useful historical introduction), E. S. Cornell, "The Radiant Heat Spectrum,"Ann. Sci., vol. Ill (1938), D. Fleming, "Intent Heat and the Invention of the

Watt Engine," Isis, vol. 43 (1952), L. Galvani, Opere edite e inedite (Bologna,

1841), D. McKie and N. H. de V. Heathcote, The Discovery of Specific and Latent

Heats (London, 1935), J. C. Maxwell, Electrical Researches of Henry Cavendish

(Cambridge, 1879), Philosophical Magazine, Natural Philosophy through the i8th

Century (Commemoration Number, 1948), A. Volta, Collezione del Opere (Fircnze,

1816), W. Cameron Walker, "The Detection and Measurement of Electric,

Charges in the i8th Century," Ann. &s.,vol. I (1936), Sir E. Whittaker, History

of Theories of Aether and Electricity, vol. I (Cambridge, 1951).

INDEX

ACADEMIES :

Accadcmia dci Lincci, 188

Accademia del Cimento, 151, 189-

191, *93 264Academic Franchise, 188, 196Academic P.oyale des Sciences, 98,

100, 186, 191, 195-8, 201, 202, 205,

2i5> 333Berlin, 201-2

Royal Society, 31, 99, 152-4, 182, 186,

189, 192-5, 198, 200, 215, 216, 241,

246, 249, 250 S 266-8, 284, 289, 309,

338, 358-9Aepinus, F. U. T. (1724-1802), physicist,

352

Agricola [Georg Bauer] (1490-1555), 70,

73, 163, 221-3, 308, 321 n.

al-Battani (d. 929), astronomer, 61, 63Albert of Saxony (13167-90), philo-

sopher, 56, 8 1-2, 83, 85Albert the Great (c. 1200-80), philo-

sopher, 28, 31, 134, 276, 278, 369A chemy, 26, 69, 223-4, 244> 249, 307-8Aldrovandi, Ulissi (1522-1605), natural-

'st, 156Alfonsine Tables, 16

Alhazen (c. 965-1040), physicist, 21-2,

251al-Razi (d. 923-4), physician, 39, 308Anatomy, ancient and medieval, 37-40and art, 41-4comparative, 145-6, 286

renaissance, 41-51, 135-6, 142-4, 148Animalculists, 291-3Animism, 12, 21, 310Apollonius of Perga (b, c. 262 B.C.),

mathematician, 126

Aquinas, Thomas (12257-74), philo-

sopher, 5Archimedes (287-212 B.C.), mathe-

matician, 9, 10, 21, 76, 124, 158, 171,

235Aristotle (384-322 B.C.), philosopher, 5,

74, 186-7,217,339as biologist, 10, 28, 37-8, 71, 129, 133,

I34 *54 156, 158, 275-7, 281-2,286, 289, 295, 297-8

381

as physicist, 12, 19, 21, 23-6, 35, 53,

56, 66 ff., 76, 78, 92, 97, 100, 103,

106, 109 ff., 114, 117, 165, 172, 206-

207, 210, 260-1, 306, 313scientific method of, 160-3, 168-9, 185

Arzachel (c. 1029-87), astronomer, 61

Astrolabe, 4, n, 14, 17, 235

Astronomy, Copernican, 3, 51-68, 108,

i 1 9, 192, 194, 261, 370-1 ; and re-

ligion, 102-6

Galilean, 107-16

Kepler's Laws, i7, 121-6, 248, 260,268

Newton and, 248Ptolemaic, 3, 11-18, 52-65; con-

stants of, 15 n.

Atomism, set Philosophy, mechanical

Averroes (b. 1126), philosopher, 138Aviccnna (979-1037), physician, 4, 39,

71, 138, 140

Avogadro, Amadeo (1776-1856), physi-

cist, 338

BACON, FRANCIS (1561-1626), philo-

sopher, 7, 31, 34, 75 n., 135, 182,

189, 192-4, 197, 201-2, 207, 211,

213, 219, 235, 243on scientific method, 161, 164-9,

173-4, 1 80, 183-5Bacon, Roger (1214-94), philosopher,

6, 22, 31, 34, 163, 306, 309Baer, K. E. von (1792-1876), biologist,

292

Baker, Henry (1698-1774), microscopist,

241

Ballistics, 78, 93, 190, 230Banks, Sir Joseph (1743-1820), natural-

ist, 191, 280, 290, 339Barrow, Isaac (1630-77), mathematician,

231, 247, 249Bartholomew the Englishman (fl. c.

1220-40), 30, 72, 278Basil Valentine, pseudonym, 69, 224Bauhin, Caspar (15601624), botanist,

131,283Bausch, Lorentz, 201

382 INDEX

Bayle, Pierre (1647-96), writer, 204Beccaria, G. B., 333

Becher, J. J. (1635-82), philosopher, 326

Beddoes, Thomas (1760-1808), physi-

cian, 325Beeckman, Isaac (1588-1637), philo-

sopher, 89-92, 93, 96, 100, 207

Beguin, Jean (c. 1550-1620), chemist,

312, 317 n.

Benedetti, Giovanbattista (1530-90),

mathematician, 78, 87

Bennet, Abraham (1750-99), 352

Bentley, Richard (1662-1742), philo-

sopher, 272

Berengario da Carpi (1470-1550), ana-

tomist, 38, 41, 44, 45, 138

Berkeley, George (1685-1735), philo-

sopher, 185

Berzelius, J. J. (1779-1848), chemist, 362

Bewick, Thomas (1753-1828), engraver,

293

Biological Illustration, 29-30, 41 ff,, 48,

71, 277, 278-9, 369

Biological Sciences :

blood transfusion, 153-4Cartesian ideas on, 148-51circulation of the blood, 141-8

evolution, 284, 296-8medieval ideas, 27-31

microscopy, 240-2, 286-7, 290 ff.

physiology, 135-41, 152-3, 287-9, 291renaissance of, 130-4, 275-84

taxonomy, 276, 281-6, 290, 294-6

Biringuccio, Vanoccio (fl. c. 1540),

metallurgist, 70, 221-2

Black, Joseph (1728-99), chemist, 82 .,

224, 308, 318, 328, 329-30, 332-4,

337 ; on heat, 344-7Boccaccio, Giovan (1315-75), 8

Bode, J. E. (1747-1826), astronomer, 126

Boerhaave, Herman (1668-1738), chem-

ist, 291, 295, 318, 328

Bonamico, 78

Bonnet, Charles ( 1 720-93) , naturalist, 241

Borelli, Alfonso (1608-79), 77, 150, 247,260

and theory of gravitation, 264-6, 267

Boswell, Sir William (d. 1649), diplomat,

192

Boyle, Robert (1627-91), philosopher,

23 n., 25, 105, 143, 151, 172, 182,

191-6, 208, 216, 219, 220, 223, 225-

226,238,291,343,365

and chemistry, 304-5, 309, 311, 313,

316-28, 333, 337, 338and mechanical philosophy, 211-13,

214and Newton, 244, 247, 272 n.

Boyle's Law, 227

Bradley, James (1692-1762), astronomer,

34<>

Brahe, Tycho, see TychoBriggs, Henry (1556-1630), mathe-

matician, 229

Brouncker, William, Viscount (1620?-

1684), P.R.S., 193 ., 194

Brunfels, Otto (1489-1534), herbalist,

131,278-9,369Bruno, Giordano (1548-1600), philo-

sopher, 55, 74, 77, 103-5

Brunschwig, Hieronymus (c. 1450-1512),

223Buffon (George Louis Leclerc, Comte de,

1707-88), 297-3Buridan, Jean (c. 1295-1358), philo-

sopher, 6, 20-21, 56Burnet, Thomas (1635-1714), divine,

297

CAIUS, JOHN (1510-73), physician, 38

Calendar, 3, 16, 53

Caloric, 328, 343-6Camerarius, Rudolph Jacob (1665-

1721), botanist, 157, 294Canano, Giovanbattista, of Ferrara

(i5i5-79) anatomist, 41, 46Cardano,Jerome ( 1 50 1 -76) , philosopher,

20, 78, 156, 163, 226

Carlisle, Sir Anthony (1768-1840), sur-

geon, 360Carnot, Sadi (1796-1832), engineer, 347

Cassini, Jacques (1677-1756), astrono-

mer, 341

Cassini, Jean (1625-1712), astronomer,

Cavalieri, Bonavcntura (1598-1647),

mathematician, 226, 227, 231

Cavendish, Sir Charles (1591-1654),

mathematician, 192

Cavendish, Henry (1731-1810), on

chemistry, 318, 328-32, 334 n., 335on physics, 272, 353-5

Celsus (fl. c. A.D. 14-27), physician, 41

Cesalpino, Andreas (1519-1603), botan-

ist, 131, 279, 283, 321 n.

INDEX 3B3

Cesi, Frederigo, Duke of Aquasparta, 188

Charles II, K. of England (1660-85),

'94

Chaucer, Geoffrey (1340?- 1400), 4

Chemistry, 24-6, 131, 212, 244, 249,

303-38electrochemistry, 360-3

iatrochemistry, 309-13, 317-18industrial, 70, 201, 220-4, 34 36~7

Christian IV, A", of Denmark (1588-

1648), 118

Clairaut, Alexis Claude (1713-65),

mathematician, 340, 341-2Clement VII, Pope (1523-34), 54

Colbert, Jean Baptiste (i6io/-83), 195,

197

Collingwood, R. G., 9

Colombo, Realdo (1516-59), anatomist,

46, 48, 142

Combustion, 324-5, 327, 330, 332-6Comenius, J. A. (1592-1671), 194 n.

Copernicus, Nicholas (1473-1543), as-

tronomer, 6, 1 6, 35, 74, 102, 108-9,

114-17, 120 ff., 163-4, 174,234,261,

263, 275

compared with Vesalius, 36-7

system of, 51-68Cordus, Valerius (1515-44), botanist,

131,279Coulomb, Charles Augustin (1736-

1806), engineer, 352-4Cullen, William (1710-90), physician,

318Cuvier, Georges (1769-1832), naturalist,

297, 30i

D'ALEMBERT (Jean le Rond, 1717-83),

mathematician, 340Dalton, John (1766-1844), chemist, 215,

326Dante Alighieri (1265-1321), 72

Darwin, Charles (1809-82), biologist,

256,275,296-8,301,341Davy, Sir Humphry (1778-1829), chem-

ist, 325, 360-2Dee, John (1527-1608), mathematician,

55, 72De Graaf, Regnier (1641-73), biologist,

292De Groot, 100De Tficlusc, Charles (1524/5-1609),

botanist, 279

De TObel, Matthias (1538-1616), natu-

ralist, 283Dcmocritus (c. 460-370 B.C.), 97, 103,

207

Desaguliers, John Theophilus (1683-

1744), physicist, 340

Desargues, Gerard (1593-1662), mathe-

matician, 191

Descartes, Ren (1596-1650), 83 n., 89-92, 93-4, 99, loo, 105-6, 113, 127,

191, 196, 198-200, 205, 215, 236,

258, 274, 297, 318, 325and biology, 1 29, 1 38, 298ideas of matter and motion, 95, 207-213

and mathematics, 227, 228, 230mechanics of, 96-8and Newton, 99, 244, 247, 270-1and optics, 251, 252 n., 254

physiological ideas of, 148-52, 157on scientific method, 164, 177-84and theory of gravitation, 260, 264-5

DeThou,J. A. (i553-!6i7), '95

Diderot, Denis (1712-84), philosopher,

339

Digges, Thomas (d. 1595), mathemati-

cian, 104Dioscorides (fl. c. A.D. 50), herbalist, 10,

217,276,277,279,281Doilond, John (1706-61), optician, 242,

342-3Dominico Soto (1494-1570), theologian,

83-5, 88, 91-2Drebbel, Cornelius (1572-1634), 192

Drury, John, 193 n.

Dryander, Johann (c. 1500-60), physi-

cian, 41, 46

Dufay, Charles (1698-1739), electrician

349-50, 362

Dumas, J. B. A. (1800-84), chemist, 292

Dupuy, 195

Diircr, Albrecht (1471-1528), 278Dymock, Cressy, 193 n.

ELEMENTS, 313-15, 320-3Aristotelcan, 1 7 ff., 23-6, 60, 208

Elizabeth I, Qji. of England (1558-

1603), 72

Ellis, John (i 7107-76), naturalist, 241,

290Ent, Sir George (1604-89), physician,

384 INDEX

Epicurus (340-270 B.C.), 97 187* 207

Ercker, Lazarus (?-i593), metallurgist,

221-2

Estienne, Charles (1504-64), anatomist,

41, 44, 46, 139Euclid (fl. c. 300 B.C.), 10, 171

Eugene, Prince of Savoy (1663-1736),202

Euler, Leonhard (1707-83), mathe-

matician, 342-3Eustachio, Bartolomeo (1520-74), ana-

tomist, 46

Evelyn, John (1620-1706), virtuoso,

193 !94 200

Experimental method, 6, 32-3, 45, 86,

99> 129-35, 145-6, 173-6, 181-3, 185,

189-91, 199, 216, 223-4, 233, 255-

257, 270, 273-4

FABRICIUS (FABRIZIO), HIBRONYMUS, of

Aquapendcnte (1537-1619), physician,

139, 286, 298Fabricius, Johann (fl. c. 1605-15),

astronomer, 108

Fabroni, Giovanni (1752-1822), 360Fahrenheit, Gabriel Daniel (1686-1736),

physicist, 238, 341, 344

Fallopio, Gabriele (1523-62), anatomist,

46,48Faraday, Michael (1791-1867), physi-

cist, 185, 332, 353, 362Ferdinand II, Duke of Florence, 190

Fermat, Pierre ( 1 60 1-65) , mathematician,

94, 191, 230, 231, 252 n.

Fernel, Jean (1497-1558), physician, 46,

Field, John (i525?-87), astronomer, 55

'''lamsteed, John (1646-1719), astrono-

mer royal, 120, 198-9, -238

Foster, Samuel (c. 1600-52), astronomer,

193

Franklin, Benjamin (1706-90), 347,

350-3, 358> 36*

Frederick I, Elector of Brandenburg andK. of Prussia (1688, 1700-13), 201

Frederick II, Emperor (i 194-1250), 28

Freind, John (1675-1728), physician,

326

Fresnel, Augustin (1788-1827), engineer,

245Fuchs, Leonard (1501-66), herbalist,

J3' 278-9, 280, 369

GALEN (A.D. 129-99), physician, 9, 10,

36. 37-5i 7i> 74 129, 131-6, 138, 141,

152,217,310,313Galileo Galilei (1564-1642), 18, 35, 45,

48* 56-7> 59> 65> 68, 98-100, 105,

106, 127, 135, 147-3, 158, 167, 182,

i8a-ox>, 194-5, 199. 207,211,217,219, 225-6, 230, 233-5, 238, 275,

301, 33*. 335 337. 365-6on astronomy, 107-17, 120/1., 121

and Descartes, 92-101

importance of, 74-7on mechanics, 78-92and Newton, 247 ., 261, 263, 270,

272scientific method of, 164, 168-78,

180-1, 183-4Galvani, Luigi (1737-98), anatomist,

355-8, 362

Gassendi, Pierre (1592-1655), philo-

sopher, 156, 157, 191, 196, 207-8, 215Geber, pseudonym, 69, 306Gemma Frisius (1508-55), astronomer,

54-5Generation, 25, 27-8, 284, 290-3, 297

spontaneous, 28, 154-7, 284, 291

Geoffrey, fitienne Francois (1672-1731),

chemist, 326Gerard of Cremona (c. 1114-87), trans-

lator, 4, 39Gcsner, Conrad (1516-65), naturalist,

279, 282-3, 298Gibbon, Edward (1737-94), historian,

339Giese, Tiedeman, 55

Gilbert, William (1540-^603), physician,

72, 86, 89, 93, 96, 185, 1 88, 192, 21 1,

235 348and gravitation, 260-2, 263

Glauber, Rudolph (1604-70), chemist,

i333"37Glisson, Francis (1597-1677), physician,

193

Goddard,Jonathan ( 1 6 1 7-75), physician,

193

Graunt, John (1620-74), statistician, 225

Gravitation, theory of, 66, 79, 86, 99,

126-8, 206, 248, 259-74, 342action at a distance, 96, 99, 127, 260,

265, 272

Gray, Stephen (d. 1736), electrician, 349

Gregory, James (1638-75), mathemati-

cian, 239

INDEX 385

Gresham, Sir Thomas (i5ig?-79), mer-

chant, 187 n.

Gresham College, 187 n., 192, 205Grew, Nchemiah (1641-1712), botanist,

157, 240, 284, 288-9Grimaldi, Francesco Maria (1613-63),

254Grosseteste, Robert (</. 1253), bishop of

Lincoln, 5-6, 22

Gucricke, Otto von (1602-86), 348Guido da Vigevano (c. 1280-1350),

physician, 7

Gttnther, Johann (1487-1574), anatom-

ist, 44. 45, 138, 140

Guy de Chauliac (d. 1368), surgeon, 71

HAAK, THEODORE (1605-90), translator,

193

Hales, Stephen (1679-1761), physio-

logist, 287, 291, 329Haller, Albrecht von (1708-77), physio-

logist, 301

Halley, Edmond (1656-1742), astrono-

mer, 1 20, 199, 246, 249, 268, 269Harriot, Thomas (1560-1621), mathe-

matician, 192, 230Harrison, John (1693-1776), horologist,

242

Hartlib, Samuel (d. 1670?), 193, 194 n.

Hartsoeker, Nicholas ( 1 656-1 725) ,micro-

scopist, 292

Harvey, William (1578-1657), physician,

^0,37,46,51, 149, 151-2, 158, 185,

192, 235, 239, 286, 298on generation, 154-7, 291, 29?on the circulation, 134-48predecessors of, 1 39-43

Hawksbee, Francis (d. 1713?), electrician,

34, 348

Heisenbcrg, Werner,, 114

Helmont, Johann Baptista van (1577 or

1580-1648), philosopher, 312-17, 319,

320. 324Henri de Mondeville (fl. c. 1280-1325),

surgeon, 40Heraclides of Pontus (c. 388-310 B.C.),

astronomer, 65 n.

Herbah, 29, 71, 131, 276-82Hero of Alexandria (ist cent. A.D.),

mechanician, 10, 207Herschel, Sir William (1738-1822),

astronomer, 242, 258 n.

Hevelius, Johann (161 1-87), astronomer,1 20, 236, 240

Hipparchus (fl. c. 161-127 B.C.), as-

tronomer, 15, 61, 118

Hippocrates (c. 460-380 B.C.), physician,

io,37Hobbcs, Thomas (1588-1679), philo-

sopher, 104, 192

Hoffman, Friedrich (1660-1742), chem-

ist, 291

Hooke, Robert (1635-1703), physicist,

ngn., 152, 194, 199,211, 219,240,246, 286, 296 /!., 298, 324-5, 343

on gravitation, 260, 264-9, 271 n.

on optics, 251-5Horrocks, Jeremiah (1617-41), as-

tronomer, 192Humanistic scholarship, 1-2, 8-10, 53,

188, 229, 279, 371-3Hume, David (1711-76), philosopher,

339Hunter, John (1728-93), anatomist, 301

Hus, John (c. 1370-1415), 2

Huygens, Christiaan (1629-95), physi-

cist, 98-9, 181-2, 190, 194 n., 195-7,

203, 232-3, 271and gravitation, 267-8, 273and Newton, 250 n.

and optics, 252 n., 255, 259

Huygens, Constantyn, 250 n.

IBN AL-NAFIS AL-QURASHI (c. 1208-88),

physician, 140

Instrument-making and Instruments, 69,

119-20, 234 ff.

air-pump, 236-7balance, 224, 235barometer, 190, 238electrical, 348-9, 352-3, 359

hygrometer, 190

microscope, 235-6, 239-41

telescope, 107, 235, 239-40, 242, 248thermometer, 190, 238

Inventions, i, 6-7, 22, 99Isidore, Bp. of Seville (c. 560-636), 278Islamic Science, 3, 4, u, 17, 21-2, 39,

53, 56, 61, 69 n., 118, 138, 140, 163 .,

220, 229, 230, 306-3

JABIR IBN HAYYA"N (fl. c. 775), physician,

37

386 INDEX

James I, A*, of England (1603-25), 192

James II, K. of England (1685-8), 249

John of Holywood (Sacrobosco) (c.

1200-50), 12

John Stephen of Calcar (6. 1499 ; d.

1546-50), artist, 48

Johnson, Samuel (1709-84), 293, 339

Johnson, Thomas (d. 1644), botanist, 156

Jordanus Nemorarius (?fl. c. 1 180-1237),

mechanician, 6

Joule, James Prescott (1818-89), physi-

cist, 256, 346

Journals, scientific, 203-4

Jung,Joachim (1587-1657), botanist, 284

Junker, Gottlob Johann (1680-1759),

physician, 326 n.

KEILL, JOHN (1671-1721), mathemati-

cian, 326

Kepler, Johann (1571-1630), astrono-

mer, 48, 68, 1 06, 108-9, i7' 185,

192 n., 226, 231, 243, 247, 260

astronomical discoveries of, 1 16-28

and gravitation, 261-5, 267

LAGRANOE, JOSEPH Louis (1736-1813),

mathematician, 340

Laplace, Pierre Simon Marquis de ( 1 749-

1827), mathematician, 274, 334, 340,

345-7Lavoisier, Antoine Laurent (1743-94),

chemist, 24, 224, 256, 293, 301and chemistry, 303, 305, 308, 316, 322,

324-5, 328, 329, 331, 332-8and physics, 345-7

Laws of Nature, 171-3Acceleration, 80, 92-4, 1 1 3

Inertia, 86-7, 89, 92-3, 96

Leeuwenhoek, Antoni van (1632-1723),

microscopist, 131, 203, 236, 241-2,

275, 286, 290, 292, 298

Leibniz, Gottfried Wilhelm (1646-1716),

201-2,204,216,273, 297and mathematics, 227, 231-2, 250 n.

Lemcry, Nicholas (1645-1715), chemist,

318Leonardo da Vinci (1452-1519), 9, 10,

20, 29, 41-2, 46, 78-9, 82, 91, 138, 163,

365Libavius, Andreas (i54O?-i6i6), iatro-

chemis^ 311-13, 317

Linnaeus, Carl (1707-78), naturalist,

i3*> 275, 282, 283, 285, 290, 293-6,

298, 34i

Locke, John (1632-1704), philosopher,

250, 274Logarithms, 229

Longomontanus, Christian (1562-1647),

astronomer, 123Louis XIV, K. of France (1660-1715),

Lower, Richard (1631-91), physician,

152-4Lucretius (c. 98-55 B.C.), poet, 9, 103,

206-7Lull, Raymond (1232-1315/16), philo-

sopher, 224Lusitanus, Amatus (151 1-68), anatomist,

39Luther, Martin (1483- 1546), reformer, 55

MACH, ERNST (1838-1916), physicist, 86

Machiavelli, Niccolo (1469-1527), 9

Maclaurin, Colin (1698-1746), mathe-

matician, 342

Macquer, Pierre Joseph (1718-84),

chemist, 308Macrobius (fl. c. 400), commentator, 4

Malpighi, Marcello (1628-94), biologist,

146, 156-7, 240, 242, 275, 286-8,

290- 1; 293Marco Polo (c. 1250-1323), i

Marcus Graecus (prob. pseudonym, c.

1300), 306

Margarita Philosophica, 1 1 ff., 20, 22-3, 26

Martianus Capella (fl. c. 470), Romanwriter, 65

Massa, Niccolo (d. 1569), anatomist, 41

44,46Mathematics, 9, u, 69, 97, 100, 126,

170-1, 178, 1 80, 192, 218, 224-34, 248Mattiolo, Pietro Andrea (1500-77),

herbalist, 279

Maupertuis, P. L. Moreau de (1698-

1759), mathematician, 341

Maxwell, James Clerk (1831-79), physi-

cist, 265 n.

Mayer, Robert (1814-87), physician, 346

Mayerne, Sir Theodore Turquct de

(1573-1655), physician, 311 n.

Mayow, John (1645-79), physician, 325,

328Mazarin, Jules Cardinal (1602-61), 196

INDEX 387

Medicine, 3-4, n, 37-5* 7O- 1 , 73

130-4, 200, 277-81, 310 ff.

Mendel, Gregor (1822-84), botanist,

i3> 275Merrett, Christopher (1614-95), physi-

cian, 193

Mersenne, Marin (1588-1648), 94, 113,

I9' *95, 196, 199

Michelangelo (1475-1564), 41

Michieli, 280

Milton, John (1608-74), 193 n., 197 n.

Mondino dei Luzzi (c. 1275-1326),

anatomist, 40, 45

Montmor, Habert de, virtuoso, 194 n.,

196, 200

Moray, Sir Robert (d. 1673), virtuoso,

193 , 194

More, Henry (1614-87), theologian, 247

Moufet, Thomas (1533-1604), physician,

156, 282

Musschenbroek, Pieter van (1692-1761),

physicist, 340

NAPIER, JOHN (1550-1617), mathe-

matician, 192, 228-9Natural History (see also Biology), 10, 25,

27-31, 71, 130, 198, 274 ff., 298-302

Navigation, 3, 6, 192, 219, 235

Neckham, Alexander (i 157-1217), philo-

sopher, 31

Needham, John Turberville (1713-81),

291

Needham, Joseph, 77 n.

Newton, Sir Isaac (1642-1727), 21, 88,

94, 102, 105, 116, 171-3. 177, 182,

198-9, 205, 216, 223, 226, 234, 275,

294. 32i, 326, 331-2, 337, 340-1,

354, 363, 365and Descartes, 99, 2 1 1

and gravitation, 263-70life etc., 244-50and mathematics, 229, 231-3mechanical philosophy of, 213-15,

270-4and optics, 239, 250-1, 254-9, 342~3

Nicholas of Cusa ( 1 40 1 -64) , philosopher,I! 59* i4 33

Nicholas of Damascus (c. 64-1 B.C.), 276 n.

Nicholson, William (1753-1815), 360Nollet, AbbiJean-Antoinc ( 1 700-70), 354Novara, Domenico Maria da (1454-

1504), astronomer, 54

OBSERVATION, accuracy of, 17, 43, 49,

52-3, 1 15, * 18-19, 167, 199, 21 7, 223-4,

353Oersted, Hans Christian (1777-1851),

physicist, 362

Oldenburg, Henry (i6i5?~77), publicist,

191* 193, 194 n -> 196,203,249Omar Khayyam (c. 1040-1124), mathe-

matician, 230Oresme, Nicole (c. 1323-82), philosopher,

6, 20-1, 24, 53, 78, 85, 87, 103, 365on diurnal rotation, 56-60variation of qualities, 80-3, 88 n., 89,

230Osiander, Andreas (1498-1552), divine,

55

Ovists, 291-3

PALEY, WILLIAM ( 1 743- 1 805) , theologian,281

Paracelsus (Theophrastus Bombastus vonHohenheim (c. 1493-1541), 70, 73-4,

132-3, 224, 304, 308-12, 218

Par6, Ambroise (1510-90), surgeon, 71,

33

Pascal, Blaise (1623-62), mathematician,

100, 101, 190-1, 195, 227Pasteur, Louis (1822-95), bacteriologist,

154, 256, 291Paul III, Pope (1534-49), 55Peiresc, Fabri de (1580-1637), virtuoso,

191

Pell, John (1611-85), mathematician,

193"-

Penny, Thomas (c. 1530-88), botanist,

282 n.

Peter of St. Omer (c. 13501400), 307Peter the Stranger (fl. c. 1270), physicist,

6

Petrarch, Francesco (1304-74), poet, 8

Petty, Sir William (1623-87), political

economist, 193 n., 194 ., 225-6Pcurbach, Georg (1423-61), astronomer,

",53Philosophy, mechanical, 9-10, 21, 97,

101, 148-51, 157, 159, 205-16, 248,

254, 259-60, 271, 274, 289and chemistry, 319-26

Philosophy of science, Baconian, 164-8,

301

Cartesian, 177-84Galilean, 168-77

388 INDEX

Philosophy of science, in Greece, 159-63

Newtonian, 255-8, 270-4

Phlogiston, 326-36Physical sciences :

Acoustics, 23, 226

Dynamics, Aristotelean, 18 ff., 52-3,

57,66-8Galilean, 78-92, 110-34, 117

Impetus theory, 19-21, 56, 78-87

Electricity, 206 ; static, 347-55 J

current, 355-63Heat, 23-4, 169-70, 190, 206, 328,

343-7

Optics, 21-3, 1 80, 209-10, 214, 235-6,

239, 245, 248, 250-9, 342-3

Magnetism, 206, 210

Mechanics, Newtonian, 245. 248,

262-74, 340-2Statics, 21, loo-ioi

Picard, Jean (1620-83), astronomer, 198,

34 1

Plantades, 292Plato (429-348 B.C.), 4, 20, 24, 162, 306Plattes, Gabriel (fl. c. 1640), agronomist,

193 n.

Pliny the Elder (A.D. 23-79), 4, 71, 217,

276, 298, 306Poisson, Sime'on Denis (1781-1840),

physicist, 354Pole, Reginald, Cardinal (1500-58), 41

Pope, Alexander (1688-1744), poet, 250Porta, Giovanbaptista (c. 1550-1615),

1 88

Power, Henry (1623-68), physician, 291

Prevost, J. L., 292

Priestley, Joseph (1733-1804), on chem-

istry, 328 ff.

on physics, 339, 352-3Proust, Marcel (1871-1922), writer, 299

Ptolemy (/. A.D. 127-51), astronomer, 12,

15-17, 21, 52 ff., 61, 63 ff., 107, 109,

117, 162

Pythagoras (?58o-?5OO B.C.), mathe-

matician, 63

RANELAOH, Countess of, 193 n.

Raphael Sanzio (1483-1520), artist, 41

Ray, John (1627-1705), naturalist, 131,

'57, 197 > 275. a8l 28*-5, 288, 294,

296, 297Reaumur, Re*ne Antoine Ferchault de

(1683-1757), 241, 290, 341

Rccorde, Robert (i5io?-s8), mathe-

matician, 55

Redi, Francesco (1626-98), physician,

130, 156-8, 284, 298

Regiomontanus (Johann Mullcr, 1436-

1476), astronomer, u, 53

Reinhold, Erasmus (1511-53), astrono-

mer, 54-5, 58Rcisch, Gregor (d. 1525), see Margarita

Philosophica

Renaissance, 6-10, 29-30Renaudot, The*ophraste ( 1 583- 1 653) ,

journalist, 195

Rey, Jean (b. c. 1582, d. after 1645),

physician, 324Rhcticus (Georg Joachim, 1514-76),

astronomer, 54, 58, 63Riccioli, Giovanbattista (1598-1671),

astronomer, 94Richelieu, A. J. du Plessis, Due de (1585-

1642), 188, 195, 196

Richmann, Georg Wilhelm (1711-53),

physicist, 351

Ritter, J. W. (1776-1810), physicist, 360Roberval, Giles-Personne de (1602-75),

mathematician, 94, 191

Robison, John (173^-1805), physicist,

353Roemer, Ole (1644-1710), astronomer,

120, 197-8

Rohault, Jacques (1620-73), teacher,

208-10

Rondelet, Guillaume (1507-66), natural-

ist, 73, 282

Rudolph II, Emperor (1576-1612), 118,

123Rufinus (c. 1350-1400), herbalist, 277>

369

SACROBOSCO, setJohn of HolywoodSaint-Hilaire, Gcoffroy (1722-1844), bio-

logist, 292Sanctorius (1561-1636), physician, 129

Sarpi, Paolo, 85

Scheele, Carl Wilhclm (1742-86), chem-

ist, 318, 328, 329 n., 330-1, 333, 334 n.

Scheiner, Christopher (1575-1650), as-

tronomer, 108

Schleiden, M. J. (1804-81), biologist, 275

Schoenberg, Nicholas, 55Science and Technology, 6-7, 218-24,

236, 347

INDEX 389

Scrvcto, Michael (1509-53), theologian,

46, 105 n., 140-2

Shakespeare, William (1564-1616), 72Slusius (Sluze, R. F. W. Baron de, 1622-

1685), mathematician, 247Sorbicre, Samuel (1615-70), physician,

9&-7

Spallanzani, Lazzaro (1729-99), bio-

logist, 154, 291

Sprat, Thomas (1635-1713), divine, 189

Stahl, Georg Ernst (1660-1734), chemist,

291, 326-8Stclluti, Francesco (1577-1653), natural-

ist, 1 88, 240Stcno (Stcnsen, Niels, 1638-86), anatom-

ist, 296 n.

Stevin, Simon (1548-1620), engineer,

loo-i, 227, 229

Stukeley, William (1687-1765), anti-

quary, 248Sturm, Christopher (1635-1703), mathe-

matician, 201

Swammerdam, Jan (1637-80), anatom-

ist, 157, 240, 286-7, 289, 290-1

Swedenborg, Emmanuel (1689-1772),

philosopher, 292

Sylvius (Jacques Dubois, 1478-1 555) ,

physician, 46

TACHENIUS, OTTO (fl. c. 1660), chemist,

318

Tartaglia, Niccolo (1500-57), mathe-

matician, 20, 78-9, 227Tclesio, Bernard (1508-88), philosopher,

63Thabit ibn Qurra (<:. 830-901), astrono-

mer, 53, 6 1

Thales (c. 640-546 B.C.), philosopher, 23

Theophilus the Monk (?y?. c. 1200), 307

Theophrastus (380-287 B.C.), herbalist,

10,28,217,275-7,279Thevenot, Melchise'dec (1620-92), 197

Thompson, Benjamin (Count Rumford;

1753-1814), 346Timocharis ofAlexandria (fl. c. 300 B.C.),

astronomer, 61

Tompion, Thomas (1639-1713), horo-

logist, 219Torricelli, Evangelista (1608-47), physi-

cist, 189, 190, 227 n., 230, 238Tournefort, Joseph Pitton de (1656-

1708), naturalist, 131, 285, 294

Transmission of learning, i, 4, 6-7

Tremblcy, Abraham (1700-84), micro-

scopist, 241, 290Tycho Brahc (1546-1601), astronomer,

52, 94, 108, 112, 123-4, I9i

192 n., 198,217,243work of, 1 1 8-2 1

Tychonic System, 65-6

Tyson, Edward (1650-1708), physician,286

ULUOH BEIGH (1393-1449), son ofTimur

Lang, 118

Universities, 2-3, 1 1, 40, 42, 131

Bologna, 3, 40, 54

Cambridge, 143, 182, 187, 246, 247,

249, 250, 269Cracow, 54Louvain, 44Montpcllier, 40Oxford, 182, 187, 190

Padua, 3, 36, 44, 47-8, 76, 139, 142-3

Paris, 3, 5, 20, 44, 48, 81, 142, 182

Pisa, 76-7, 109

Salerno, 39

Wittenberg, 54

VALVERDE DR AMUSCO, JUAN (fl. c. 1 540-

1560), anatomist, 142

Vesalius, Andreas (1514-64), anatomist,

9, 35-5i> 7<>> 7i 74. I4<>-1 163, 217,

235

compared with Copernicus, 36-7on the heart, 139

Viete, Fran9ois (1540-1603), mathe-

matician, 228

Viviani, Vincenzo (1621-1703), mathe-

matician, 76 n., 189

Volta, Alessandro (1745-1827), physi-

cist, 357-60, 362

Voltaire, Francois Marie Arouet de

(1694-1778), 274, 293, 339

WALLB, JOHN (1616-1703), mathe-

matician, 193, 247

Watson, Richard (1737-1816), divine,

327Watt, James (1736-1819), engineer,

347

Wesley, John (i 703-91 ), 339

390 INDEX

Whiston, William (1667-1752), divine, Wolff, Caspar (1738-94), biologist, 293

297 Wordsworth, William (1770-1850), 293

White, Gilbert (1720-93), naturalist, Wren, Christopher (1632-1723), archi-

293, 299Wilkins, John (1614-72), divine, 103,

193, 194William of Moerbeke (c. 1215-86),

translator, 39William of Ockham (c. 1295-1349),

philosopher, 56, 163

Willughby, Francis (1635-72), naturalist,

284Wilson, George (1631-1711), chemist, 3 1 8

tect, 153, 194

Wyclif,John(</. 1384), 2

YOUNG, THOMAS (1773-1829), physicist,

245

ZALUZIAN, Adam Zaluzanski of (c. 1500-1610?), botanist, 281

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